Technical Report: A Limnology Study

The purpose of this report is to present the findings of a limnological study done at the confluence of the Salmo and Pend d'Oreille Rivers, which now make up part of the Seven Mile Dam Reservoir. A previous study was completed in the summer of 1974 in order to determine whether a game fishery existed, and, if it did, whether it would be harmed by the construction of the Seven Mile Dam. Conditions in the Seven Mile Dam Reservoir, on the Pend d'Oreille River, are much the same now as they were prior to the construction of the Seven Mile Dam. Although access to the Salmo River spawning grounds has been made easier, oligotrophic conditions prevail and there is a lack of plankton, benthic organisms, and rooted aquatic vegetation. These are significant factors when considering the survival of any game fish, including rainbow trout, which are already present in the Salmo River, and have the potential for moving into the reservoir. Another study or series of studies should be conducted during various other times of the year to determine whether the lake will retain its oligotrophic nature, or whether it will slowly improve.