In this paper we aim to define whether fish farms or stocked trout streams substantially contribute to the diet of otters Lutra lutra living in freshwater habitats of Mid-Finland. Diet was assessed using spraint analysis. We especially focused on areas with fish farms and stocked trout Salmo trutta streams (salmonid-rich habitat) and used ‘normal’ (salmonid-poor) habitats as control. Frequency of salmonid remains in spraints was significantly higher in salmonid-rich habitats than elsewhere in all seasons, the difference increasing from summer to winter. In salmonid-rich habitats, however, salmonid consumption was not strongly seasonal. Data from spraint collection indicated a shift in activity towards salmonid-rich habitats in winter. Otters therefore seem to switch prey seasonally, due to seasonal variation in the availability of other prey categories, by choosing to forage in particular, predictable habitats. Furthermore, our results suggest that, in salmonid-rich habitats, the increase in salmonid frequency is to a larger extent due to the presence of fish farms than that of trout streams. Fish farms, and to a lesser extent stocked streams, may therefore constitute seasonally important feeding grounds for otters.