Geostatistical calculations were applied to the results of an echo-integration survey on Lake Annecy, France, in order to determine estimates of fish biomass. Initial sampling along transects, which was systematic but not exhaustive, did not allow the satisfactory adjustment of variograms. A special sampling method was necessary. The survey gave an estimate of biomass with a confidence limit of ±20 %. An optimal sampling procedure in lakes is proposed within the framework of geostatistical calculations.