Summary:

Detailed hydrological and biological studies were carried out in 2002-2005 on chosen, typical reaches of Wkra River, representing middle-sized lowland one. The results show that the biodiversity of the riverbed does not depend on the fact of river regulation as itself, but on the presence of unique, repeatable microhabitats of peculiar hydromorphological parameters. The relationships between the microhabitat types and invertebrate taxa were analysed. The paper shows the results of those analyses and the divagations about possible connections of microhabitats, invertebrates and mosaic of river eco-systems.