Water release through the dam, additionally determined by the functioning of a wild-water slalom canoeing track, strongly modified natural discharge of the lowland Drzewiczka River, contributing to a considerable heterogeneity of environmental conditions; the biota, their resource and their habitats were distributed as patches. Having more physically heterogenous environments this section of the Drzewiczka River contained a greater abundance of macrobenthos than streams with less heterogeneous habitats, chironomid insects being dominants, and ephemeropterans and trichopterans eudominants. Over the annual cycle much difference in the distribution of trichopterans was recorded. In the reophilous habitats scrapers represented by Psychomyia pusilla (up to 6500 inds m-2 in December), and filtrators of the family Hydropsychidae � Hydropsyche contubernalis (up to 2400 inds m-2 in June) and Hydropsyche pellucidula and Hydropsyche modesta were the most abundant. The habitat overgrown by submerged macrophytes was represented by the same species that occurred in the riffle, but in much lower abundance. In the stagnant habitat infrequent case trichopterans, such as Mystacides sp., Anabolia nervosa, and caseless ones, Lype reducta and Cyrnus sp., were recorded. In this very mosaic river section, which is 160 m in length, 16 trichopteran taxa were noted.