On the occasion of the International Day for Biological Diversity, the LIFE RESQUE ALPYR project highlights one of the major conservation challenges facing mountain aquatic ecosystems: the loss of biodiversity caused by the introduction of fish into lakes where they were not originally present.

High-altitude aquatic ecosystems are highly valuable reservoirs of biodiversity. Despite harsh environmental conditions, they host highly specialized biological communities adapted to cold, nutrient-poor waters and strong seasonal fluctuations. It is precisely this specialization that also makes them particularly vulnerable to any disturbance.

One of the most significant transformations has been the introduction of fish, mainly for recreational purposes. This process began centuries ago with the translocation of native trout from nearby rivers, but it intensified during the second half of the 20th century with the introduction of other non-native species such as minnows, used as live bait in sport fishing.

The ecological impact of these introductions goes far beyond simply adding a new species

Fish prey heavily on insect larvae, aquatic invertebrates, and amphibians, disrupting the food web and altering the functioning of the entire ecosystem. The consequences include algal proliferation, reduced oxygenation and water transparency, and the disappearance of species characteristic of these habitats.

However, the effects are not limited to the aquatic environment. Many terrestrial species depend on insects emerging from these lakes as a food resource, meaning that these imbalances can also affect birds, bats, and small mammals.

In response to this situation, ecological restoration has become a key tool

The LIFE RESQUE ALPYR project, coordinated by CEAB-CSIC, is working to restore these ecosystems in the Pyrenees and the Alps by removing introduced fish and monitoring the recolonization by native fauna.

This is a slow and technically complex process. Depending on the type of introduced species and the characteristics of each lake, restoration may require several years of continuous fieldwork.

To assess biodiversity recovery, scientific teams combine classical monitoring techniques with advanced molecular tools such as environmental DNA (eDNA). This technology makes it possible to detect the presence of species from fragments of genetic material they leave in the water, without the need for direct observation.

In addition, the analysis of sediments accumulated at the bottom of lakes offers an exceptional historical perspective. This natural archive allows researchers to reconstruct what biodiversity was like before human disturbances and to better understand how far present-day ecosystems have diverged from their original state.

Marking the International Day for Biological Diversity, the project’s principal investigator, Teresa Buchaca, explains in this video why preserving high-mountain aquatic biodiversity is essential for maintaining the ecological balance of these unique ecosystems.

The insects that inhabit lakes are often larval stages that will metamorphosize and eventually emerge as flying adults. On land they are a vital food source for many terrestrial animals living around the lakes. Fish heavily predate on insect larvae, consequently reducing the number of insects that make it out of the water. This could result in less food for insectivores, such as spiders, predatory beetles and centipedes that live around these lakes.

As a part of the Life RESQUE ALPYR project, we studied 12 high mountain lakes in the Western Italian Alps. Four lakes were fishless, four lakes were undergoing fish removal, and four still had established fish populations. We placed traps near the lakes shore and farther away to capture ground-dwelling invertebrates, and we also sampled insect larvae to assess the prey availability, i.e. emerging insects.

What did we find?

Compared to lakes with fish, fishless lakes had much more emerging aquatic insects, confirming that fish reduce an important food source for animals on land. We also found more ground-dwelling predators near the lake shoreline, suggesting their habitat preference and importance of lake insects as a food source.

Interestingly, we didn’t observe any big differences in ground-dwelling predator numbers between lakes with and without fish. This suggests that while aquatic insects play a role in shaping nearby terrestrial communities, other factors may also influence predator abundance, and that more lakes are needed in future studies to get a clear picture of this relationship.

Although more research is needed to fully understand the impact of introduced fish on ground dwelling predators, our study highlights the important connection between lake and surrounding land ecosystems. Changes in one environment often trigger to responses in the other and understanding these relationships is essential in designing effective conservation strategies for these unique high mountain areas.

This news results from the Master’s Degree Project in Biology (2025) by Gea Lukšić (Department of Biology, Lund University), carried out under the guidance and supervision of Rocco Tiberti and Lucia Bello (Department of Biology, Ecology and Earth Sciences (DiBEST), University of Calabria) and Anders Persson, Department of Biology (Lund University).

In the Colomers cirque in the Aran Valley, salmonids have been successfully eradicated from Gargolhes Lake, and eradication of Cabidornats Lake is expected to be confirmed this summer. These results, combined with the successful use of chemical methods in Manhera Lake, would mean that the objectives for this sector have been met.

In the Dellui valley (Ribagorça), minnows have been eradicated from Upper Dellui Lake, and work will continue to fully eradicate the trout population.

Work will also continue across the different sectors of Pallars Sobirà to achieve the objectives set for each lake.

In Muntanyó Lake, trout removal efforts are ongoing after having eradicated the minnow population this year—one of the initial targets. In Naorte Lake, where a drastic reduction in the minnow population has been achieved over time, further work will still be needed to ensure complete eradication. In the Peguera valley, efforts also continue in Coveta and Llastra lakes, where the population of introduced salmonids has already been greatly reduced.

Equally noteworthy is the success achieved in the lakes of Tres Estanys del Mig and Tres Estanys de Baix, where chemical eradication methods have been applied to remove introduced fish. These lakes are now considered free of introduced fish.

Across all lakes included in the project, very significant improvements have been observed in invertebrate and amphibian populations, as well as gradual increases in water transparency, whenever the presence of introduced fish has been reduced or eliminated.

The pilot test, which will start this week, aims to eliminate introduced species and restore the ecological balance of these high-mountain ecosystems. The trial will involve the use of rotenone, a biodegradable ichthyocide. The results of the action will provide essential data to evaluate the effectiveness and safety of this product, contributing to the development of safe protocols for the application of piscicides to mitigate the impact of introduced species, such as minnows, in high mountain lakes.

The initiative is part of a broader strategy to restore high-mountain aquatic habitats within the framework of the LIFE RESQUE ALPYR project, with the aim of converting the restored lakes into biodiversity reserves and ecological corridors.

The environmental impact of minnows in high mountain lakes

One of the main threats to high mountain lakes is the presence of introduced fish, which reduce the biodiversity of native species and disrupt the balance of the ecosystem.

Among the introduced fish species, minnows (Phoxinus spp.) have the greatest ecological impact and also pose the greatest challenge for demographic control. It is a small cyprinid with rapid growth and a high reproductive rate, highly adaptable and capable of forming dense populations.

Conventional capture techniques used to remove fish from high-mountain lakes do not always yield satisfactory results when minnows are present. For this reason, it is necessary to explore alternative methods.

A Pioneering Initiative

Rotenone is a natural, biodegradable ichthyocide extracted from various tropical and subtropical plant species of the legume family. These plants, along with others with toxic properties such as those of the genus Verbascum, have traditionally been used for fishing in rivers and lakes around the world, depending on the plant species available, including in the Pyrenees.

In the environment, rotenone degrades rapidly, persisting for only a few days or weeks. To date, its use as an ichthyocide has been primarily applied in North America, Australia, New Zealand, the United Kingdom, and northern Europe—especially Norway—with some isolated experiences in the rest of Europe, including Spain.

The LIFE RESQUE ALPYR features two pilot trials using rotenone, pioneering actions in the context of high-mountain lakes in Europe.

The first of these trials took place in 2024 at Lake Manhèra (Val d’Aran). This is the only precedent so far for the application of rotenone in a high-mountain lake in Europe. The intervention was successful, as the minnows were eradicated and the lake is currently recovering its biodiversity, with the recolonisation of amphibians and various invertebrates, such as certain dragonflies, which had disappeared due to the introduction of the minnow.

In the Tres Estanys area, two applications are planned: the first at Lake Tres Estanys del Mig, scheduled between September 2 and 4, and a few weeks later at Tres Estanys de Baix. The goal is to restore the ecological integrity of these sites and to increase knowledge about the use of rotenone in a more complex scenario, acting on two lakes whose combined volume is three times that of Lake Manhèra.

The intervention will be carried out by Sorelló, Estudis al Medi Aquàtic, S.L. and Associació La Sorellona, under the scientific coordination and supervision of the Centre for Advanced Studies of Blanes (CEAB-CSIC) and the Institute of Environmental Diagnosis and Water Studies (IDAEA-CSIC), with the direct support of the Alt Pirineu Natural Park and Forestal Catalana. The entire process will be monitored with visits from specialists from Norway, a leading country in this type of application, and through a rigorous monitoring program to ensure the safety and effectiveness of this innovative technique.

Nothing exceptional so far—except that these might be the first Rana temporaria tadpoles to complete metamorphosis in Lake Leità in many decades!

Since the 1960s, the lake had been colonized by an introduced population of brook trout, a salmonid native to North America, introduced into several park lakes at a time when the devastating effects of fish introduction into these ecosystems were still unknown. Among these effects, the presence of fish tends to prevent Rana temporaria from reproducing in the same environments due to predation on both tadpoles and adults.

However, since 2023, an ecological restoration action has been underway at Lake Leità as part of the LIFE RESQUE ALPYR project, aiming to return the lake to its natural, fish-free condition. This year, the project team is working to remove the last remaining brook trout individuals, but the first positive effects of the eradication are already becoming visible. As early as 2024, unusual movements of frogs had been observed around the lake… these few tadpoles might be the first of many new generations of Rana temporaria in this lake!

Image of Lac Leità, in Parco Nazionale del Gran Paradiso

On 6 May, the Pyrenean Institute of Ecology (IPE-CSIC) in Jaca (Aragón) hosted a new session of the Itinerarios Cicerón, an initiative launched by the Spanish National Research Council (CSIC) to bridge scientific knowledge with society and to promote evidence-based decision-making. This edition focused on biodiversity recovery and science-based actions for nature restoration.

Teresa Buchaca, researcher at the Centre for Advanced Studies of Blanes (CEAB-CSIC), contributed as an expert in high mountain aquatic ecosystems, which are central to the LIFE RESQUE ALPYR project. In her talk, she explained that high mountain lakes function as true natural laboratories, as they allow researchers to track human impacts over time through palaeoecological analysis. This historical perspective is key to understanding ecosystem changes and planning more effective restoration measures.

As a successful example, Buchaca presented LIFE RESQUE ALPYR, a project aimed at restoring the ecological functionality of mountain lakes in the Pyrenees. She outlined actions such as removal of invasive species and the restoration of natural cycles, which have shown proven effectiveness and are based on the scientific knowledge generated at CEAB-CSIC and by the project’s partner institutions.

The event also featured CEAB researchers Jordi Pagès and Daniel Oro, who shared their insights on the restoration of coastal and delta ecosystems. In addition, pre-recorded videos were shown, offering a glimpse into the researchers’ work in the lab and in the field.

The session brought together scientists from various CSIC centres, nature reserve managers, public authorities, civil society organisations, businesses, and journalists. Coordinated by Graciela Gil-Romera (IPE-CSIC) and Óscar Godoy (EBD-CSIC), the organisers emphasised that nature restoration is an ecological imperative, and can only be successful if grounded in robust and applicable scientific knowledge.

The Itinerarios Cicerón initiative aims to connect research teams working on similar topics and to translate their findings into practical knowledge for society, helping to effectively address today’s environmental challenges.

More information is available at this link.

They’re everywhere, but they’re small. Sometimes not so small as to be invisible: with a bit of patience and good lighting, some can be spotted with the naked eye as tiny moving specks in the water. But to truly appreciate their unusual shapes and diversity, you need a closer look. Under the microscope, a world full of bizarre structures and creatures is revealed —many of them seemingly from another planet.

In this post, we invite you to discover some of these fascinating little inhabitants of alpine lakes.

• Alona

This small cladoceran lives in the littoral zone of the lake, near the shore. The specimen shown here is a female carrying a large egg in a dorsal pouch. She keeps it protected there until the offspring is fully developed —an effective strategy in cold, unpredictable environments.

• Cyclops abyssorum

Measuring about 2 mm in length, this predatory crustacean is easily recognized by its single large eye on top of its head —hence the name. It lives near the bottom of the lake. Although its long antennae look menacing, they aren’t used for hunting: the male uses them as clasping tools during courtship.

• Keratella cochlearis

At first glance, it looks more like a flower than an animal. This tiny rotifer, just 0.1 mm long, swims in search of microalgae and bacteria, propelled by a ciliated organ near its upper spines.

• Daphnia longispina

This species can grow up to 2.5 mm, and its large compound eyes give it an almost endearing expression when seen under the microscope. It is one of the most common cladocerans and a key species in lake food webs, thanks to its voracious appetite for algae.

• Chydorus sphaericus

Round and charming, this is the smallest crustacean in the group, measuring between 0.2 and 0.5 mm. It is a cosmopolitan species and considered the most widespread cladoceran in the world, found in a wide variety of freshwater habitats.

High mountain lakes, natural ecosystems that originally did not contain fish, have undergone drastic changes due to the introduction of non-native species, primarily trout and minnow. This introduction has caused significant predation of the native fauna, profoundly altering the ecological balance of these lakes.

The study that Dr. Ventura presents analyzes the impact of these introductions on cladocerans, such as Daphnia, in the high mountain lakes of the Alps and the Pyrenees. The results indicate that lakes with minnow have suffered a more severe impact on Daphnia populations.

As part of the conservation projects – LIFE BIOAQUAE, LIFE LIMNOPIRINEUS, and LIFE RESQUE ALPYR – both trout and minnow have been eliminated or are being eliminated from 32 high mountain lakes in the Catalan Pyrenees and the Italian Alps.

Preliminary evaluations show that Daphnia populations have recovered in most lakes where they were previously absent. Additionally, the eradication of minnow has been accompanied by an increase in species richness, as well as the appearance of planktonic species and those associated with macrophytes.

Throughout the congress, there will be a total of 65 oral presentations and 41 posters, as well as two keynote lectures. The contributions will cover a wide range of topics related to the biology of cladocerans, including our beloved Daphnia, as model organisms. Topics such as ecology, evolutionary biology, genomics, interaction with environmental stress factors, diversity, biogeography, and systematics will be addressed.

One of the main threats to these ecosystems is the presence of introduced fish species, such as trout and, especially, the common minnow, which outcompete native species and severely disrupt the balance of ecosystems. Therefore, one of the key actions of the project is the restoration of 22 high mountain lakes in the Pyrenees and the Alps by eliminating introduced fish using traditional techniques.

Rotenone: An innovative solution

Conventional fish capture techniques, such as nets, traps, and electrofishing, are commonly used for fish removal in mountain lakes. However, biological and environmental constraints, such as the size of the lake or the presence of minnows, can limit their effectiveness. For this reason, exploring alternative methods is necessary.

The common minnow, a small cyprinid with rapid growth, high reproductive rate, and great adaptability, can form dense populations even in extreme conditions, making population control challenging. In this context, a pilot test has been conducted using rotenone, a natural biodegradable ichthyocide extracted from the roots of plants in the Fabaceae family, traditionally used for fishing in Southeast Asia and South America. It is similar to troca or Verbascum, a plant historically used for fishing in ponds and streams in the Pyrenees, though now its use is prohibited.

In the environment, rotenone degrades quickly, persisting only a few days or weeks. So far, its use as an ichthyocide has been concentrated in North America, Australia, New Zealand, the United Kingdom, and northern Europe, particularly in Norway, with some isolated experiences in other parts of Europe, including Spain.

Pioneering application in high mountain lakes of the Pyrenees

The pilot test was carried out in a lake located in the peripheral area of the Aigüestortes and Estany de Sant Maurici National Park (PNAESM), in the Aran Valley. A strategically located body of water was chosen, as there are no lakes or large upstream watercourses that could pose a risk of fish reintroduction after the intervention, nor that would hinder the application of the product without affecting nearby habitats.

The experiment will provide crucial data on the effectiveness of this substance in a new biogeographic context. The entire process will be monitored through a rigorous follow-up program, ensuring the safety and efficacy of this innovative technique.

The operation was carried out by Sorelló, Estudis al Medi Aquàtic, S.L. and the LSorellona Association, with the coordination and scientific supervision of the Centre for Advanced Studies of Blanes (CEAB, CSIC) and the Institute of Environmental Diagnosis and Water Studies (IDAEA, CSIC), with the direct support of the Aran Council, Forestal Catalana, and the Aigüestortes and Estany de Sant Maurici National Park (PNAESM).

LIFE RESQUE ALPYR

This is a LIFE project aimed at the recovery of mountain aquatic habitats by improving the conservation of various habitats and species in four Natura 2000 sites in the Alpine biogeographic regions of the Pyrenees (northeast Spain) and the Alps (northwest Italy) (www.liferesquealpyr.es).

The project is co-financed by the European Union’s LIFE 2020 program, which promotes conservation and habitat and species restoration actions in protected areas within the European Natura 2000 network. In the Catalan part of the project, participants include the Department of Territory, Housing, and Ecological Transition of the Generalitat de Catalunya, the Conselh Generau d’Aran, the University of Barcelona, the IDAEA-CSIC, the companies Forestal Catalana and Sorelló Estudis al Medi Aquàtic, and the La Sorellona association. On the Italian side, partners include the Mont Avic Nature Park, the Università degli Studi di Pavia, the Università della Calabria, and the Water Research Institute of the National Research Council (IRSA-CNR). Additionally, the Andrena Foundation, the Gran Paradiso National Park, and the municipalities of Espot and Lladorre are participating as co-financiers.

Despite the temptation to take a dip, it’s important to remember that, in general, swimming in high mountain lakes is prohibited. High mountain lakes are not pools or natural beaches; they are quite the opposite. They are unique aquatic environments with high natural value. These ecosystems have a notable diversity of species.

A unique and fragile ecosystem

Characteristics such as altitude, water chemistry, or size determine the species that can live there. From organisms that live suspended in the water as part of the plankton (algae, water fleas, and copepods), to plants, mollusks, worms, insects, and amphibians that live on the bottom or the shoreline, to birds and bats that feed on insects emerging from the water.

Furthermore, many high mountain lakes are located within Natural or National Parks, making them especially protected areas with specific regulations governing activities that can affect wildlife species.

Swimming severely disrupts the balance of these ecosystems

High mountain lakes are very sensitive to changes; therefore, any disturbance can alter their ecological state. When we swim in a lake, we leave behind residues, toxins, and even viruses or bacteria that affect the fauna and flora living there.

When we enter the water, we stir up sediments from the bottom, causing the lake to become fertilized. As a result of the excessive availability of nutrients, microalgae grow excessively, decreasing the oxygen in the water and its transparency. This is what we call fertilization due to human frequentation.

Many of the animals living in the lakes, such as amphibians, are especially sensitive, as they can absorb toxic chemicals through their skin. Products like sunscreens and insect repellents are harmful to these species.

Amphibians are also sensitive to certain viruses or fungi of which humans and livestock are carriers. By stepping into the lake, we transfer them to the water and, consequently, to all the fauna, especially species like the midwife toad.

We should not allow pets to swim either. Dogs, when entering the water, also stir up the bottom, and the anti-parasite collars they wear contain toxic substances for wildlife.

What do we do at LIFE RESQUE ALPYR?

Environmental education and public awareness play a key role in the preservation of natural spaces and are one of the pillars of the project.

We not only organize outings and talks for all types of audiences but also produce educational materials (posters, brochures, newsletters, or videos) to explain the importance of high mountain aquatic ecosystems and what needs to be done to preserve them.

The most ambitious actions of the LIFE RESQUE ALPYR project include the eradication of mink in medium-sized lakes in both the Pyrenees and the Alps to promote the recovery of amphibian populations, small semi-aquatic mammals such as the Pyrenean desman or the water shrew, and some species of bats and the lacustrine habitat.

The actions to achieve this have proven effective, as they were successfully tested in the research projects preceding ALPYR, namely, LIFE LIMNOPIRINEUS and LIFE BIOAQUAE.