Abstract
Parallel determinations of phytoplankton biomass and chlorophyll‐α concentration were carried out on five reservoirs. Highly significant positive correlations between phytoplankton biomass values and chlorophyll‐α values were found. The possibility of finding a conversion factor linking these two parameters is discussed. The chlorophyll content per unit phytoplankton biomass encountered during the period of study in all reservoirs varied between 0.14 and 3.41% of fresh weight. The influence of light intensity, nutrient concentration and species composition on chlorophyll content per unit phytoplankton biomass is considered.