The distribution of Trichoptera within 13 microhabitats and against 11 environmental variables (physicochemical, structural and related to shoreline/watershed usage) was studied in a small reservoir in northern Poland. Caddisflies were examined at multiple organization levels (trichopteran assemblages, diversity indices and three functional groups). A total of 38 taxa were recorded. Significant correlations with physicochemical properties of water were found for 13 species. According to the RDA, the environmental parameters explained 33 % of the caddisfly variance and six groups of Trichoptera were determined based on habitat features. However, the RDA based on richness and diversity metrics and functional groups of Trichoptera explained 46.5 % of the variance. Temperature, dissolved oxygen, electric conductivity, shading, abundance of helophytes and shore/watershed usage were significant determinants of caddisfly distribution. In general, micro-distribution of Trichoptera can be used to detect various environmental and, to a lesser extent, usage gradients. Among all levels of caddisfly organization, rheophiles showed the most pronounced response. We conclude that, despite the anthropogenic origin and management of impoundments, such small lowland waters can be important for maintaining high biodiversity of Trichoptera and serve as an important secondary habitat since they have been found to provide numerous and diversified microhabitats for their development.