Diurnal and diel vertical distribution of limnetic zooplankton species in relation to temperature and dissolved oxygen profiles was examined at a central station in Lake Naivasha. During calm days thermal stratification developed gradually from late morning to reach maximum formation at mid-day. Dissolved oxygen concentrations showed similar vertical profiles to temperature. These stratifications were, however, short lived and were broken up in late afternoons by the wind induced poly-holomictic nature of the lake. During the day most zooplankters aggregate at the top 3–4 metre zone of the water column coincident with maximum photosynthetic activity. The pattern of diel vertical distribution of zooplankton in Lake Naivasha is undefinedly even. The absence of significant diel changes in the distribution of the limnetic zooplankton may be related to the absence of permanent physico-chemical boundaries and lack of predation pressure in the open water.