The intervention will take place at Tres Estanys del Mig and Tres Estanys de Baix, within the Parc Natural de l’Alt Pirineu, with the dual objective of ecologically restoring these lakes and deepening the study of the effectiveness of rotenone —a biodegradable ichthyocide— as a tool for controlling introduced species. This is the second application of its kind in the Pyrenees, following the successful operation carried out in 2024 at estany Manhèra (Val d’Aran).
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 turning the restored lakes into reservoirs of biodiversity and ecological corridors.
The problem of the minnow
One of the main threats to high-mountain lakes is the introduction of fish species, which reduce the diversity of native species and alter the balance of the ecosystem.
Among these fish is the minnow (Phoxinus spp.). It is the species with the greatest ecological impact and, at the same time, the most difficult to control demographically. It is a small cyprinid with rapid growth and a high reproductive rate, showing great adaptability and forming dense populations.
Conventional capture techniques used for eliminating fish in high-mountain lakes do not always yield satisfactory results when minnows are present. For this reason, it is necessary to explore alternative methods.
Rotenone: an innovative solution
Rotenone is a natural biodegradable ichthyocide extracted from various species of tropical and subtropical plants belonging to the legume family. These plants, and others with toxic properties such as those of the genus Verbascum, were traditionally used for fishing in rivers and ponds around the world depending on the plant species available, including in the Pyrenees.
In the environment, rotenone degrades quickly, persisting for only a few days or weeks. Until now, its use as an ichthyocide has been concentrated in North America, Australia, New Zealand, the United Kingdom, and Northern Europe, especially Norway, with some occasional experiences in the rest of Europe, including Spain.
The LIFE RESQUE ALPYR project foresees two pilot tests with rotenone, pioneering actions in the context of Europe’s high mountains. These actions are intended to provide crucial data to assess the effectiveness and safety of this product, contributing to the development of safe protocols for the use of piscicides —a strategic step to reverse the impact of minnow introduction in high-mountain lakes.
Pioneering pilot tests with a strong demonstrative component
One of these two pilot tests has already been carried out, in 2024 at estany Manhèra (Val d’Aran). This is, to date, the only precedent of rotenone application in a high-mountain lake in Europe. The operation was successful, as the minnow was eradicated and the lake is now recovering its biodiversity, with the recolonisation of amphibians and various invertebrate species such as dragonflies that had disappeared following the introduction of the minnow.
In the Tres Estanys area, two applications are planned: a first one in the estany de Tres Estanys del Mig, and a few weeks later, in the estany de Tres Estanys de Baix. The objective is the ecological restoration of these sites, as well as to expand knowledge on the use of rotenone in a more complex scenario, acting on two lakes whose combined volume is three times that of estany Manhèra.
The intervention will be carried out by Sorelló, Estudis al Medi Aquàtic, S.L. and the Associació La Sorellona, with scientific coordination and supervision from the Centre d’Estudis Avançats de Blanes (CEAB, CSIC) and the Institut de Diagnòstic Ambiental i Estudis de l’Aigua (IDAEA, CSIC), with direct support from the Parc Natural de l’Alt Pirineu and Forestal Catalana. The whole process will be overseen by specialists from Norway, a leading country in this type of application, and through a rigorous monitoring programme to guarantee the safety and effectiveness of this innovative technique.
The LIFE RESQUE ALPYR project
This project aims to restore mountain aquatic habitats by improving the conservation of various habitats and species in four Natura 2000 sites in the alpine biogeographical regions of the Pyrenees and the Alps.
It is co-financed by the LIFE 2020 programme of the European Union, which promotes actions for the conservation and recovery of habitats and species of flora and fauna in protected areas within the European Natura 2000 network. It is coordinated by the CEAB-CSIC. On the Catalan side, project partners include the Departament d’Agricultura, Ramaderia, Pesca i Alimentació de la Generalitat de Catalunya, the Conselh Generau d’Aran, the Universitat de Barcelona, the IDAEA-CSIC, the companies Forestal Catalana and Sorelló Estudis al Medi Aquàtic, and La Sorellona.
On the Italian side, partners include the Mont Avic Natural Park, the Università degli Studi di Pavia, the Università della Calabria, and the Istituto di Ricerca Sulle Acque del Consiglio Nazionale delle Ricerche (IRSA-CNR). In addition, the Fundació Andrena, the Gran Paradiso National Park in Italy, and the Espot Town Council and Lladorre Town Council participate as co-financiers.
