Data on fish status and water chemistry of lakes in southern Norway have in previous investigations been used to delineate the influence of water quality on the survival of fish populations in acid environments. These analyses generally point to pH and the concentrations of inorganic aluminium species and calcium as the main determinants of fish status. However, these investigations have either been carried out by a series of bivariate statistical methods or not included all potentially important variables.

In the present investigation, data from a number of these earlier studies have been pooled and reanalysed by different bivariate and multivariate statistical methods. The dependent variable in the analyses has been fish status for brown trout, and possible independent variables have been 14 chemical and physiographical variables which include the concentration of all major chemical species in the water, lake size and lake altitude.

The bivariate analyses confirmed previously observed correlations between trout survival and each of the independent variables. In different stepwise multivariate analyses, however, only pH, concentration of inorganic aluminium and lake altitude entered the regression equations, and in that order.

The results also show that low calcium concentration, within the range found in lakes in southern Norway, is neither harmful per se for the survival of trout populations, nor does calcium protect the fish from the deleterious effects of inorganic aluminium.