Invasive species removal in progress at Laihalampi in Nuuksio – use of pond prohibited until 14 September 2025
Work is underway to remove an invasive fish species called the pumpkinseed (Lepomis gibbosus) from the Laihalampi pond, located in the Hakjärvi nature reserve in Nuuksio. The City of Espoo and the Uusimaa Centre for Economic Development, Transport and the Environment are in charge of the project. The pond has been treated with a chemical solution, and the use of the pond is prohibited from 11 August to 14 September 2025. The aim is to prevent the spread of the pumpkinseed and its negative effects on other species.
The fish are being removed using a biodegradable rotenone-based solution. Laihalampi was treated with the solution on 11 August 2025, and therefore the use of the pond is prohibited until 14 September 2025. Fishing and swimming in the pond are not allowed, nor should pets be allowed to swim in or drink from the pond. Visitors are also advised to avoid the Laihalampi loop on the Sorlampi nature trail during this period.
Rotenone is toxic to fish and other aquatic organisms, but less harmful to mammals and birds. Rotenone breaks down in a few weeks and, when diluted in water, does not pose a risk to human health. If you come into contact with Laihalampi pond water during this time and develop symptoms, contact the Poison Information Center(external link, opens in a new window) (tel. +358 800 147111) or seek medical attention immediately.
Operation helps preserve large ecological area
The pumpkinseed is a North American fish species known for its bright colours and popularity as an aquarium and pond fish. Within the EU, it is classified as an invasive species, and it is prohibited to import it into the EU or release it into the environment.
The pumpkinseed weakens the living conditions of native species by reducing their living space and increasing competition for food. It defends its territory aggressively and reproduces and spreads efficiently. This leads to the disappearance of other species and the deterioration of biodiversity.
Removing the pumpkinseed from Laihalampi is especially important because the pond is connected to a larger body of water. If the invasive species spreads to Lake Pitkäjärvi in Nuuksio and beyond, it will pose a major threat to the biodiversity of the local waters.
“Several alternatives were considered for removing the pumpkinseed, but due to the pond’s location and surrounding terrain, these were found to be extremely difficult, if not impossible, to implement. Using rotenone is the most cost-effective and lowest-risk option in terms of preventing the spread of the species,” says invasive species specialist Paula Salomäki from the Uusimaa ELY Centre.
Do not release invasive species into the wild
Because the pumpkinseed is classified as an invasive species, it is prohibited to import, breed, sell or possess it or release it into the environment. In addition to penalties prescribed by law, those responsible for spreading the species may be required to cover the costs of removal. In the case of Laihalampi, the total cost is around EUR 10,000.
“Removing invasive species from water bodies is often challenging – and therefore also expensive,” Salomäki says.
Report invasive species sightings
Successful control of invasive species depends on continued reporting through the website: vieraslajit.fi. When possible, include a photo of the sighting.
An invasive species is a plant, animal or other organism that has been moved – either intentionally or unintentionally – outside its natural range by human activity. Invasive species threaten biodiversity and related ecosystem services.
Learn more about the pumpkinseed at vieraslajit.fi.(external link, opens in a new window)
Report a sighting through vieraslajit.fi.(external link, opens in a new window)
More information:
Uusimaa ELY Centre – customer service for environmental matters: ympariston.asiakaspalvelu@ely-keskus.fi
City of Espoo – Urban Environment Customer Service, tel. +358 9 81625100