Comprehensive approach to the rehabilitation and management of Vesijärvi, a lake in southern Finland

The rehabilitation programme of Vesijärvi, a lake in southern Finland, was commenced in 1987. It has been carried out in three stages: (1) reduction of the external nutrient loading to the lowest possible level, (2) management of the foodweb structure to reduce internal nutrient loading, and (3) measures to maintain the rehabilitated state of the lake. The recovery of Vesijärvi has proven biomanipulation to be an applicable rehabilitation method for large lakes, too. The mechanism behind the recovery was linked to migrations of the dense roach (Rutilus rutilus L.) population that transferred nutrients from the littoral to pelagic zone. Biomanipulation decreased the migrating fish stock and diminished both input and availability of nutrients in pelagic water. Consequently, the productivity of planktonic algae and especially cyanobacteria decreased. To maintain the achieved state, local people have been encouraged to participate in lake and drainage area management. Participation of the key groups (fishermen and farmers) has been enhanced with computer simulation models, which have been used to demonstrate the effects of fisheries and farming practices on the lake. The yield-recruit model and the multispecies value-per-recruit model have helped fishermen in optimising the fisheries to a sustainable level. With the help of the GLEAMS model, farmers have been able to compare the nutrient-loading effects of different field-farming techniques and to choose the less-loading alternatives. The increased participation and cooperation of local people and authorities has been considered to keep the comprehensive management process on a sustainable basis.