Biodiversity is declining globally, and lotic environments have not been spared from this problem. In rivers, one of the key causes of biodiversity loss is river damming and its consequences. Habitat offsetting is a way to mitigate biodiversity loss, in which habitat loss in one location is compensated in another. In lotic environments, habitat offsetting can be done using a variety of measures, e.g. mitigation habitat in bypass by a dam or a hydropower plant. In this thesis, a constructed channel in Imatra called Imatra City Brook (ICB) and its brown trout (Salmo trutta L.) population were studied. ICB was built partly to compensate the loss of riffle habitat caused by the Imatrankoski hydropower plant. The emergence period for brown trout fry was estimated and also redd and parr and density and survival were estimated. These indices were compared to natural streams; emergence period and redd density were compared to rivers Partakoski and Läsänkoski, and parr density was compared to streams Kiertojoki and Saajoki. The emergence period did not differ from natural streams, and parr density was significantly higher in ICB than in the reference streams. Redd density was similar to Läsänkoski. Based on the similarity in emergence period and high parr density, ICB seems to meet the needs of brown trout sufficiently and offers a considerably good compensation habitat. However, ICB is a small compensation habitat compared to the area and flow lost under the adjacent hydropower plant.