Beaver activity impacts communities of aquatic invertebrates. Damming typically leads to an increase of lentic (slow or motionless water)-dependent species, like dragonflies, oligochaetes, snails and mussels, at the expense of lotic (rapid water) species like black flies, stoneflies and net-spinning caddisflies. Beaver floodings create an increase in dead trees which benefit terrestrial invertebrates like "Drosophila" flies and bark beetles, which live on dead wood. The presence of beavers can increase wild salmon and trout populations, and the average size of these fish. These species use beaver habitats for spawning, overwintering, feeding and as refuges from increased water flow. The positive effects of beaver dams on fish appear to outweigh the negative effects, such as inhibition of migration. Beaver ponds have been shown to be beneficial to frog populations by protecting areas for larvae to mature in warm water. The slow-moving and standing waters of beaver ponds also provide ideal habitat for freshwater turtles.