We studied cladoceran species richness, community composition, habitat preference and density in three spatial habitats over 1 year at Thale-Noi, a large shallow tropical lake in southern Thailand. Monthly sampling conducted with activity traps deployed overnight in littoral (Hydrilla and Ceratophyllum beds), open water (Hydrilla beds) and marginal zone (Utricularia beds), revealed that the macrophyte beds support similar cladoceran diversities regardless of the habitat. Total species richness in all studied habitats ranged between 30 and 34 species, supporting up to 22 species in a trapping area of 0.09 m 2 at peak times, the majority belonging to the Chydoridae. In total, 40 species were recorded over the year, half of which were chydorids. Mixed cladoceran densities reached maxima of 160 333 ind.m x2 for a single habitat at a given moment. The dominant species included Chydoridae (Anthalona, Kurzia, Dunhevedia and Ephemeroporus), Daphniidae (Ceriodaphnia), Macrothricidae (Macrothrix) and Ctenopoda (Latonopsis). Monthly variation in species richness was most obvious in the littoral zone, whereas monthly variation in densities occurred at all sites. Community composition and habitat preference were mainly structured by depth and pH, resulting in different assemblages per habitat, but with uniform communities in the littoral (Hydrilla and Ceratophyllum) beds in a single area. This study presents the first ecological survey of Cladocera using activity traps in a shallow tropical lake.