Two echo-integration surveys were carried out in Lake Sainte-Croix with an interval of 14 months, and differences in the spatial distribution of the fish population are described. One survey was during, the other after, the spawning season of the bleak (Alburnus alburnus (L.) ), which is the predominant pelagic fish in the lake. Different methods of calculation were used to estimate the average biomass: parametric and spatial statistics. The estimates are close, but only the geostatistical estimate provides a useful confidence interval less than 20% of the estimated mean. The geostatistical variograms can be processed following a linear or a spherical model. Knowledge of fish population distributions and of natural phenomena in the lake leads to the choice of the linear model. The linear variogram takes into account the heterogeneity of the spatial distribution of the fish population and the spatial correlation of the samples.