Assessment and management of effects of large hydropower projects on aquatic ecosystems in British Columbia, Canada

Most of the hydropower generated in Canada’s western province of British Columbia is generated by a small number of large storage or diversion projects that impound large rivers. All but one were built between 1950 and 1985; a period when environmental considerations for large projects were evolving to present-day social, political and regulatory standards. Large projects result in ecosystem transformations; river valleys are converted to reservoirs, and the release of water for power generation results in highly altered flow regimes downstream of dams. I describe the effects of three projects on aquatic ecosystems and measures that have been taken over the past 60 years to monitor and mitigate those effects, with an emphasis on downstream effects to fish populations. I briefly review methods that were used to predict effects, particularly on key fish species, and consider the role of adaptive management and its alternatives on resolving uncertainties about ecological effects of large hydroelectric projects.