Researchers are sounding the alarm about a decline in plant and animal populations in Finland’s rivers, stream and its 188,000 lakes.
More than half of underwater species have become rarer in some areas, including some previously common species, say researchers at the Finnish Environment Institute (Syke).
"In areas with intensive land use, negative impacts are clearly visible. For example, in small streams affected by forestry, more than 50 percent of common species have declined," Syke researcher Anna Suuronen tells Yle News.
"The overall condition of freshwater systems varies significantly by region, with some lakes and rivers remaining nearly pristine," she adds.
Suuronen is a co-author of a landmark report published on Friday by the institute, which provides the first-ever snapshot of the state of biodiversity in Finnish lakes and streams.
The report warns that the biodiversity of inland waters has significantly declined – but also recommends measures to reverse the trend.
"People have had to change their fishing habits"
The decline in underwater wildlife is clear to the fishing community, says Juha Ojaharju, fishing specialist at the Finnish Federation for Recreational Fishing (FFC).
"In discussions with our members, it often comes to light that certain fish species are rarer than before, so people have had to change their fishing habits," he says.
"Many people don’t want to fish for species that have become endangered or threatened. Responsible fishing is becoming more important than ever. Competition for dwindling resources has increased, for example in the salmon fishery," Ojaharju tells Yle News.
The fresh report provides concrete evidence to back up anecdotal observations from those out in boats hoping for a bite.
"We collected species data from thousands of water bodies and modelled the natural species composition. For the first time, we are able to assess the state of species diversity at the national and regional level," explains Jukka Aroviita, the lead researcher on the project.
The key takeaway, says Suuronen, is that some forestry and farming practices are contributing to the degradation and loss of biodiversity – but that the situation could be improved by better land use planning and more effective buffer zones between fields and streams, for instance.
In areas affected by forestry, the worst situation is in small streams in Central and Eastern Finland. Last year, large numbers of freshwater pearl mussels were destroyed by a logging operation in Suomussalmi, eastern Finland.
"Agriculture and forestry both require large areas where the land is heavily modified. This leads to runoff into bodies of water, causing nutrification and browning of the water, for example. These environmental changes can lead to shifts in species composition and a decline in biodiversity," she explains.
That includes populations of benthic animals, such as crustaceans, worms, clams and snails, which live on or near the bottom of bodies of water. The study also surveyed mosses and other aquatic plants as well as phytoplankton, diatoms and other algae in streams and lakes.
"Our most precious natural resources"
To some, those fluctuations may seem abstract. So why should the general public care?
"The existence of a single aquatic invertebrate species may seem insignificant to the average person, but it isn’t. The decline in the diversity of basic aquatic organisms, such as benthic animals and other aquatic invertebrates, directly affects the wellbeing of fish stocks and their diversity," says fishing expert Ojaharju.
Suuronen agrees, pointing out that "well-maintained freshwater systems provide clean water for drinking and irrigation, offer recreational opportunities such as fishing and swimming, and contribute both aesthetic and ecological value for everyone who appreciates nature."
"Biodiversity itself holds intrinsic value, and inland waters may be among our most precious natural resources," she says.
What, then, are the most important things that should be done to reverse the decline?
"Biodiversity assessments should be more closely integrated into planning, implementation, and impact monitoring for water protection, conservation, and restoration," she replies. "That could prevent biodiversity decline and improve the state of degraded habitats."
Careful land use planning is also essential to mitigate runoff from surrounding areas into waterbodies, say the Syke scientists. They emphasise that proper buffer zones between areas of intensive land use and aquatic ecosystems can effectively reduce the flow of nutrients and protect water quality.
Ojaharju agrees that "the most important thing is to significantly reduce the load on water bodies from agriculture and forestry" – adding that fish migration barriers built in rivers should also be removed.
'Good ecological status' isn’t necessarily good enough
Finland is currently preparing for its national implementation of the EU Nature Restoration Law, which aims to halt biodiversity loss.
Suuronen says that achieving this goal requires that the definition of 'good ecological status' in freshwater ecosystems actually ensures the protection of biodiversity.
"Our study suggests this is not always the case: we observed significant changes in species prevalence, including declines in up to two-thirds of some population units, even in streams and lakes that are classified as having good ecological status," she says.
In other words, current guidelines may not fully safeguard freshwater biodiversity.
In Suuronen's view, "these criteria should be revisited and refined to better support restoration objectives".
The EU Nature Restoration Law requires member states to restore at least 20 percent of their degraded land and sea areas by 2030, with the goal of restoring all degraded ecosystems by 2050. The law entered into force in August 2024.
National restoration plans must be completed within two years from then, so Finland must present its plan to the European Commission by next summer.
