One in five Finnish lakes in poor condition

One in five lakes in Finland are officially classified as being in poor ecological condition, according to a report by Yle.

The classification assesses how much human activity, such as agriculture and forestry, has disrupted lake ecosystems. Factors include bottom-dwelling organisms, plant life, fish populations, and chemical measurements. Poorly rated lakes may suffer from eutrophication, excessive plant growth, cyanobacterial blooms, or reduced biodiversity.

While most lakes still receive a good rating, Finnish waters have darkened significantly since the 1990s. This trend, linked to climate change and land use, reduces light penetration, threatening aquatic life. Current ecological assessments do not fully account for the risks of darkening, which can deplete oxygen at lake beds and reduce species diversity.

Human activity remains the primary stressor on water systems. Nutrient runoff from fields and forested areas, as well as extensive ditching in peatlands for forestry, degrades water quality. Although mitigation efforts, such as buffer zones and precise fertilizer timing, can help, agriculture remains the largest source of pollution.

Climate change further complicates the picture, with warmer, wetter winters increasing nutrient leaching. While lake conditions have not significantly worsened since the early 2000s, experts warn that maintaining stability requires action. Rivers and coastal waters fare worse, with nearly half of rivers in poor condition and most coastal areas falling short of targets.

Yle’s search tool allows users to check the ecological status, phosphorus load, turbidity, and algae levels of local lakes, though data is limited for the smallest bodies of water.