Abstract. The relationship between ostracod occurrence and water quality is investigated in the Ouseburn (Newcastle upon Tyne, NE England) in both a spatial and temporal context. For the first time, ostracod assemblages are used alongside traditional biological water quality indices. Physico-chemical parameters of the water are used in conjunction with standard macro-invertebrate-based biological indices (BMWP, ASPT) to assess general water quality. This is also the first detailed study of ostracod occurrence within a small urban catchment. Ostracod, macro-invertebrate and environmental samples were taken during the summer of 2001, with a small number of late autumn replicates taken to characterize the impact of known pollution events. The pollutants encountered in this study are primarily organic in nature and include sewage, agricultural sources (such as slurry) and de-icer runoff from the local airport. The head-water and tributaries are generally characterized by good water quality despite a number of pollution events recorded during the study. Ostracod diversity and abundance, although often low, support the evidence from the traditional methods of water quality assessment, both of which decrease downstream. An inverse relationship observed between ostracod abundance and macro-invertebrate indices suggests that relatively clean-water macro-invertebrate assemblages out-compete the ostracods or may be preying upon them.