The effects of climate warming, eutrophication, air pollutant inputs and forestry activity that occurred before La Mauricie National Park was created influenced and continue to influence today water quality in the park. These stress factors threaten the natural evolution of aquatic ecosystems. On several small lakes, the quality of the habitat has not ensured the maintenance of the eastern brook trout population and has decreased the beaver population. In order to monitor the aquatic ecosystems, sampling of a number of predetermined lakes is being carried out and water quality is being measured by evaluating parameters related to acidification, eutrophication, general water quality, and oxygen and temperature conditions.