One of the most notable species in the stream is the rare stone loach ("Barbatula barbatula") attracted by the strong current and stony bottom of the stream. During dry periods sections of Igelbäcken dry up which is the most important threat to the fish. While its presence in the stream is still considered as threatened, the numbers of individuals increased during the period 1999-2001. Other fishes in the stream include perch, northern pike, roach, tench, crucian carp, and, more rarely, trout. European crayfish were observed in 1989 and signal crayfish, illegally introduced during the 1990s, is feared to threaten the population of stone loach and to bring crayfish plague into the stream.