The restoration of the lake begins

Lake Tuusula Water Protection Assosiation was founded in 1965 and it finally started to take action to save the lake in the early 1970s. As the oxygen level of the lake only seemed to get worse some aerators were purchased and they started operating early winter in 1972. They operated all winter and were powerful enough to keep the oxygen level satisfactory. Since then, the aerators have been operating every winter and the resuscitation still continues to be necessary. Aeration is important especially for the water layers near the bottom of the lake: if the level of oxygen drops the nutrients in the bottom silt, such as phosphorus, starts to be released in the water and they increase the algae production. The extra oxygen provided by aeration keeps this process in check.

The next big step on the lake’s path to recovery came in 1979, when the sea sewage that carried wastewaters from the town of Järvenpää to Helsinki to be treated was completed. It was funded by The Federation of Municipalities for Water Protection.

The main load in the eutrophication of the lake was thus removed. Now only the non-point loading of the lake remained; the load carried by streams and drains and brought on by run-off from agricultural land and wastewaters from households that remained without municipal sewage disposal.

The worst was now over but the lake still remained overly eutrophicated, as it basically still remains today. The phosphorus loading of the lake in the late 1970s was nearly 10 tons, but dropped to half with the sea sewage. However, the nutrient loading of the lake is still two times bigger than the lake’s condition could bear.

Beginning of page