The return of the whitefish: a successful ecological engineering action at lake scale (le Bourget)

Abstract

The large Alpine lakes provide many ecosystem services like supporting, provisioning, regulating, cultural and recreational. They are subject to many pressures, from global to local, from their watershed (e.g. nutrient flows, pollutant fluxes and demography) and internal (like fishing, water abstraction and recreational uses). Given their size, maintenance or restoration of the services is possible only through strong and long-term actions. Lake Bourget was impacted in the 1950s by high phosphorus loading, due to urban wastewater discharges associated with an increase in population and a change in the way of life, causing algal blooms and threatening the survival of fish species. Significant work was undertaken between 1974 and 1979 to bypass treated wastewater to the River Rhône and to improve wastewater treatment plants (phosphorus removal). Meanwhile, the fish stocking was carried out in the 1980s, particularly to support whitefish stocks. These actions have been successful. In terms of chemical quality, the drastic lowering of P concentrations has allowed a restoration to good quality water. With this improvement and stocking efforts, whitefish is now abundant, with a satisfactory natural reproduction.