Mayflies (order Ephemeroptera) are widely distributed and commonly used in biological assessment of water quality because of their sensitivity. Their application as bio-indicators in tropical streams and rivers, however, is hampered by lack of adequate information about their status in many such ecosystems. The current study investigated their species composition, distribution and abundance in relation to land use and water quality characteristics of the Thika River, Kenya. The Thika River emanates from the Aberdare Ridges and flows through forest, agricultural and urban catchments. Sampling was carried out at three sites representing forest, agricultural and urban land use systems. Dissolved oxygen, conductivity, total dissolved solids, temperature and transparency were measured in situ at each sampling station. Macroinvertebrates were sampled using a modified Hess sampler and the Ephemeropterans were later identified and sorted in the laboratory. Thirteen Ephemeroptera genera belonging to six families were obtained. Mean larvae abundance was 1 238 ind. m−2. Acanthiops (70.4%) and Afronurus (13.3%) dominated the community at all sites. The current study revealed that decreasing Ephemeroptera taxa abundance along the river channel indicates decreasing water quality.