These lakes, which are generally located under an altitude of 300 meters, are rarely acidic. They can be found near Rouyn-Noranda or north of this city. The spatial variability of surface water quality depends on physical characteristics of the land and the inputs of airborne pollutants. Thus, lakes from the Laurentian Highlands show pHs ranging from 5.5 to 7.0 units, along with low alkalinity, basic cations and conductivity levels. Lakes from the Lowlands show a greater level of water mineralization.
Acidic precipitation has a marked effect on the spatial distribution of sulphate in lakes.
However, this gradient has decreased however since 1982, following the implementation of the emission reduction programs. Most of the other water quality variables have not shown any particular trend. Their acidity comes mostly from deposition of acidifying substances received in the last century, even though the acidity of several of these lakes was in some way affected by a natural component related to organic matter. The Noranda Project also enabled us to analyze the data from ten walleye lakes located in the Belleterre sector, which is 125 to 150 km south of Rouyn-Noranda. This sector is known to be highly affected by chronic acidification problems.