Blue River and Cougar Reservoirs are proposed for modification to their withdrawal structures to allow selective withdrawal. The purpose of the proposed modifications is to improve downstream temperatures for the cold water fishery in the McKenzie River. The Corps committed to study water quality at the reservoirs to predict downstream impacts to water quality in the McKenzie River as a result of selective withdrawal. Proposed modifications to the project structures at Blue River and Cougar Lakes will result in release of warmer surface water during the spring and summer. Assuming that the current limnological structure of the lake is maintained, the present absence of strong chemical trends is unlikely to result in future increases in outflow chemical concentrations. Indeed, turbid releases may be decreased or postponed until later in the season during the release of the deeper water. The chemical trends that exist tend toward greater concentrations with depth. Surface releases may improve the water quality in these outflows.