Efforts to save the lake

Planning and experiments for the improvement of the condition of Lake Tuusula and Lake Rusut is led by the Central Uusimaa Federation of Municipalities for the Water Protection and has been in progress for over ten years. There is no easy medicine to restore the lakes but instead various different methods have to be used and all separate sides have to work together towards the common goal.

The following is a brief introduction of the planned actions to be taken for the improvement of the state of the lake. Most of them are commonly used around the world in restoring lakes.

 

Directing extra water

The diversion of extra water to Lake Tuusula through Päijänne water tunnel and Lake Rusut since 1992 has clearly improved the condition of Lake Rusut. For several years an amount equalling to its total water volume has been diverted from Lake Päijänne to the other lakes. Despite this, Lake Rusut suffers each summer from blue-green algae blooming because of its internal loading. The extra water from Päijänne water tunnel makes up about 10% of the total intake of the water of Lake Tuusula.

 

Submerged weir

Regulation of the water surface of Lake Tuusula begun in 1969 because of the water supply needs of Helsinki and in the beginning of the 1990s it was adjusted to better accommodate fishing and use of the shores.

Replacing the regulating dam with a submerged weir, as the Uusimaa Regional Environment Centre has suggested, would mostly benefit fishing and other recreational use of the lake. The construction of a submerged weir would cause somewhat more flooding in the Tuusula River valley and therefore some cleaning of the river and other restorations would be necessary. The restoration of Tuusula River is due to start in the near future but replacing the dam with a submerged weir will be still be reconsidered after the Administrative Court accepted a complaint concerning it.

 

Aeration

Since May in 1998 Lake Tuusula has been more efficiently aerated with the use of submergible Mixox aerators that aerate the deep basins and circulate the water. The experiment started as it was discovered that nearly every summer the oxygen level of the water at the bottom of the lake dropped heavily. The oxygen deficiency is caused by long warm periods when the water masses become layered and dead algae sinks to the bottom using up the oxygen of the water together with the putrid mud.

 

Restoration of the shores

Lake Tuusula project funding has also been used to annually dredge the shores of the lake, to mowing common reed and to remove vegetation such as hornworth and filamentous algae. Some of the efforts are also part of Life-project.

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