In 2012, a systematic review was conducted on the impacts of beaver dams on fishes and fish habitat (biased to North America (88%)). The most frequently cited benefits of beaver dams were increased habitat heterogeneity, rearing and overwintering habitat as well as flow refuge, and invertebrate production. Impeded fish movement because of dams, siltation of spawning habitat and low oxygen levels in ponds were the most often cited negative impacts. Benefits (184) were cited more frequently than costs (119).Kemp, P.S., Worthington, T.A., Langford, E.L., Tree, A.R.J. and Gaywood, M.J., (2012). "Qualitative and quantitative effects of reintroduced beavers on stream fish". Fish and Fisheries, 13(2): 158–181
