Naantali lake to undergo unprecedented third chemical treatment
Friday 14th August 2026 on 14:45 in
Finland
Rymättylä Kirkkojärvi, a lake in Naantali, is set to undergo chemical treatment for the third time, Yle reports. No other lake in Finland has undergone as many treatments, according to the local Kirkkojärvi association.
The association has applied for an environmental permit to treat the lake with polyaluminium chloride. The Permit and Supervisory Agency has asked Naantali’s environmental board for a statement on the application.
The lake was Finland’s first body of water to be restored with chemicals when it was treated with polyaluminium chloride in 2002. A second treatment took place in 2005 using ferrous sulphate, but the results were limited, according to Kaija Heikkinen, chair of the Kirkkojärvi association.
Heikkinen said the lake remained in good condition for 15 years, but has deteriorated in recent years. Blue-green algae appeared before Midsummer this year, and she described the lake as unusable in its current condition.
The association aims to carry out the next treatment in autumn 2027. The treatment is estimated to cost about 100,000 euros, while preliminary studies have been budgeted at 50,000 euros.
The association has received grants from several sources, including the City of Naantali, a regional vitality centre, a local insurance company and banks. Previous restoration work was financed through grants, but the association now also needs financial support from residents and holiday-home owners.
Measures have also been taken to reduce the lake’s nutrient load. Nutrients flowing from drainage ditches are considered one cause of the lake’s poor condition. Wetlands have been built in two ditches, and a third is due to be completed this autumn. The fish population has also been reduced through management fishing.
Heikkinen said it was unclear whether the third chemical treatment would be the last. The association has discussed with experts how many treatments the lake may require and whether it could eventually remain clean. She said the lake is effectively a test case because no other lake has undergone chemical treatment as many times.