Total dissolved solids (TDS) and chlorophyll a were not related in 25 lakes which were all off the Precambrian Shield. Both on-shield and off-shield lakes were included in the previous reports which showed a significant relationship between TDS and productivity. When data from on-shield and off-shield lakes were analyzed separately, there was no significant positive relationship between TDS and lake biomass or productivity. It was also shown that mean depth ([Formula: see text]) was as good a predictor of fish production as the TDS: [Formula: see text] ratio, the morphoedaphic index.Key words: TDS, biomass, productivity, morphoedaphic index, chlorophyll a, lakes