The spring overturns of Lake Nuasjärvi and Lake Jormasjärvi completed as expected 20.6.2017 14:52

The natural spring overturns of Lake Nuasjärvi and Lake Jormasjärvi were completed as expected this year as well.

“According to measurement results, Lake Nuasjärvi has overturned at the turn of May and June, during the weeks 21–23. The overturn seems to have been partially incomplete only on the bottom of an approximately 30-metre depression. At Lake Jormasjärvi, the overturn was completed well in the week 22,” says Veli-Matti Hilla, Terrafame’s Chief Sustainability Officer.

In northern areas, lakes naturally have heat layers during the winter and spring time. The layers disperse in the spring and the autumn and the bottom of the lake gets oxygen and the surface gets nutrients. The seasonal changes in weather affect the success of full overturns. If the spring is warm and calm, summer layering is formed quickly and the spring overturn may be partially incomplete. In the autumn, freezing of the surface water is usually slower, so the autumn overturn typically takes longer and overturns the water more efficiently.

Terrafame constantly monitors the condition of the lakes near the mine and plant area, in accordance with a monitoring programme approved by the responsible authority. The monitoring is based on water samples taken in field studies which are analysed in an accredited laboratory. In addition, the company has three automatic measuring points at Nuasjärvi and one automatic measuring point at Jormasjärvi.

Based on the monitoring results, the condition of both Jormasjärvi and Nuasjärvi is good, and they suit recreational purposes very well. The metal concentration of the fish of the lakes is constantly monitored, and they do not differ from the level generally found in the area.


Terrafame Ltd. is a Finnish multi-metal company producing nickel, zinc and cobalt at its mine and metals production plant located in Sotkamo. Our aim is to conduct environmentally sustainable, safe and profitable operations.

Article subjects: EnvironmentTerrafame