Specific conditions in urban areas favour to large species richness, these are also places prone to human pressure. As a result, many studies of aquatic habitats in urban ecosystems are carried out. The aim of the study was to investigate the diversity of diatom assemblages developing in artificial environment in relation to water chemical parameters. The study was performed on a small outflow of water in south-eastern Poland, which started in the storm sewage. Water at the studied sites was characterized by alkaline pH and low content of nutrients. The values of other chemical parameters were highly variable depending on the research season. A total of 113 taxa were identified in five research seasons and most of them prefer circumneutral and fertile habitats, with a high content of biogens and are tolerant for water pollutions. In analyzed materials aerophytic and terrestrial taxa were observed in high diversity.