Littoistenjärvi
Varsinais-Suomi
Littoistenjärvi is a 147.5-hectare lake situated in the village of Littoinen, straddling the municipalities of Kaarina and Lieto in Southwest Finland. The lake has an average depth of about two meters and a maximum depth of three meters, with approximately six kilometers of shoreline. It features two small islands and one islet. The shores on the Kaarina side are developed into residential areas, while the Lieto side remains forested. Motorized water traffic is prohibited year-round to preserve the natural environment. The lake faces ecological challenges typical of nutrient overload, including mass occurrences of cyanobacteria (blue-green algae) during summer, excessive growth of submerged plants like Elodea canadensis, and oxygen depletion under ice in winter. These issues have reduced its recreational use. Notably, Littoistenjärvi was the first Finnish lake where the invasive species Lagarosiphon major was found. Since 2006, management fishing has been conducted to improve water quality. In 2017, a chemical treatment using polyaluminum chloride was applied to bind phosphorus, temporarily improving water clarity. However, by mid-2024, the lake's condition had declined again with returning algae blooms and dense vegetation. Despite environmental pressures, Littoistenjärvi remains a valued natural feature in the region.
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Tip: Visitors should note that motorized boats are not allowed on Littoistenjärvi at any time, preserving the tranquility and natural state of the lake. The best time to visit is outside the summer months when cyanobacteria blooms are less prevalent. Checking local environmental reports before planning recreational activities is advisable. While the lake has limited recreational use due to ecological issues, walking along the forested shores on the Lieto side offers a peaceful nature experience. No specific ticketing or reservations are required as it is a natural site.
Interesting facts
- •Littoistenjärvi covers an area of 147.5 hectares with an average depth of about two meters.
- •The lake has two small islands and one islet within its waters.
- •Motorized water traffic is banned on the lake throughout the year to protect its environment.
- •It was the first lake in Finland where the invasive aquatic plant Lagarosiphon major was discovered.
- •In 2017, a chemical treatment using polyaluminum chloride was applied to reduce phosphorus and improve water clarity temporarily.
- •Five tons of dead fish, mainly bream, were removed following the chemical treatment in 2017.
History
Littoistenjärvi has long been a natural landmark on the border of Kaarina and Lieto municipalities.
Over recent decades, the lake has suffered from nutrient pollution leading to ecological imbalances such as cyanobacteria blooms and invasive species introduction.
Since 2006, active management including fishing and chemical phosphorus binding treatments has been implemented to restore water quality.
Despite these efforts, the lake's ecological health has fluctuated, reflecting ongoing environmental challenges common to shallow lakes in populated areas.