Aquatic Coleoptera in shallow lakes associated with the Canal de Castilla (Palencia Province, Spain) in the northern Iberian Meseta were sampled over the course of a year (spring 1998-winter 1999). These waterbodies are typical plateau wetlands with dense vegetation and vary in permanence and area (from 3.3 ha to 29.35 ha). Oxygen concentration, conductivity and pH were recorded at the time of sampling. Lake area, depth, water permanence and type of vegetation were also taken into account. Ninety two species were collected. Species richness was high in comparison with other wetlands in Spain. The assemblage structure was assessed in terms of three community parameters: richness, abundance and diversity (Shannon index). Their relationships with environmental variables were explored using correlation coefficients. The assemblage composition was analysed by multivariate techniques. First, the sites were classified by means of TWINSPAN. The presence of each species in the different TWINSPAN groups was used to assess their habitat preferences. Second, the sites and species were ordinated by Detrended Correspondence Analysis (DCA) using the CANOCO statistical package. Richness was significantly correlated with water permanence, conductivity and aquatic macrophyte cover. The first DCA axis was significantly correlated with water permanence and conductivity, but not with any of the other parameters. Conductivity was significantly inter-correlated with permanence. Therefore, water permanence and aquatic vegetation cover seem to be the main factors influencing richness, but only water permanence appears to determine species composition.