Significant amounts of algae have returned to Littoinen lake in southwestern Finland, the lake's management board announced on its website, adding that visibility in the lake has dropped dramatically.
A comprehensive chemical scrub of the lake, carried out in 2017 by the Finnish Environment Institute Syke, initially appeared to remove the algae which had been monopolising oxygen in the body of water and killing off plant life and fish. The process also returned the lake to its pristine crystal clear condition, and it became a local tourist attraction.
However, later in the same year, reports began to emerge of a large number of dead fish ound in the lake.
In November 2018, the lake became overrun by waterweed, a freshwater vegetation widely regarded to be poisonous in Finland and other parts of the world.
Swimming not recommended
The management board's announcement detailed how algae began to build up over the midsummer weekend, and that visibility in the water was down to half a metre in some parts. In addition to the detection of green algae, a strain of blue algae has also been found.
Johanna Mäkinen, head of the environmental health care department in the nearby municipality of Lieto, said that health supervisors are carefully monitoring the situation.
"There is a lot of blue-green algae in the lake, which is why bathing is not recommended," Mäkinen added.
The Littoinen lake management board received a 100,000-euro grant from the Ministry of the Environment in June in order to continue monitoring and analysing the effects of the chemical treatment.