Dams affect fish species in some obvious ways. These effects, and their proposed solutions, are often simplifications of complex systems that ignore more subtle effects. This talk will explore six ways in which dams can influence fish and fisheries. These influences include: 1) restriction of access to habitat 2) injury and mortality for migrating fish, 3) delay in migration, 4) shift in community structure, 5) shift in population demographics and 6) influence on a host of ecological services. Examples will be drawn from the Penobscot River impoundments in Maine – as well as from recent dam removals in the system.