Dam development caused physical changes in the Columbia River system. Two major physical changes are described. Key biological information on the effects of these changes on Snake River chinook salmon (Oncorhynchus tshawytscha) is reviewed. Effects on other species, such as steelhead (Oncorhynchus mykiss) and sockeye salmon (Oncorhynchus nerka), and on other stocks such as Mid-Columbia chinook, are not separately addressed, though many of the problems are the same. Present and future mitigation for these effects is discussed.