Research on the structure of sediments was carried out in 2015 in the river Krąpiel and its tributaries. The main objectives of this study were to classify the types of sediments with grain size analyzing according three different criteria, as well as influence of the substrate on the abundance and diversity of macrobenthic organisms, and to determine the quality of the ground for natural breeding of salmonids. It was found that according to Polish standards, bottom sediments of the Krąpiel river and its tributaries belong to the coarse – gravel type or sandy – gravel type, whereas according to the method used in Anglo-Saxon countries – these are sandy sediments. It was also shown that the grain size of bottom sediments of the Krąpiel river and its tributaries determine friendly living environment for macroinvertebrates and for breeding salmonids.