EFFECTIVENESS OF WATER RELEASE AS MITIGATION FOR HYDROELECTRIC IMPACTS TO FISH

Utility companies release water to mitigate the effects of hydroelectr ic projects on fish habitats. Utility companies, government agencies, and research communities in Canada, the United States, Europe, New Zea land, and Australia were surveyed as part of a Canadian Electrical Ass ociation study to evaluate the effectiveness of water release as a mit igation. Respondents identified only 28 projects in which water was re leased specifically to protect fish habitats. Fewer than half of these projects (12) were judged as being effective. Six case histories with preimpact assessment and postimpact monitoring were reviewed. In four cases fish habitat or fish populations or both were maintained; in tw o cases they were not. The effectiveness of water release differed amo ng rivers and fish species, and was greatest when designed to meet the habitat requirements of each life-history stage. A review of the lite rature did not support the theory that a particular fraction of the me an annual now provides the best fish habitat. Although smaller changes in the now regime had smaller effects, increasing minimum flows above those historically observed did not necessarily increase fish product ion.