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WATER QUALITY IN ISLAND PARK RESERVOIR, IDAHO 1981
Description:
Idahos Island Park Reservoir area (17040202) offers recreational opportunities, although water quality is impaired by nuisance algal blooms and occasional high fecal coliform bacteria counts. The fecal coliform bacteria observed in Island Park Reservoir probably originate from inadequately treated sewage at recreational facilities in the area (Forsgren et al., 1971; EPA, 1976). Unacceptable bacterial counts will be a recurring problem in scattered areas of the reservoir until adequate sewage treatment facilities are installed. Algal blooms are stimulated by an average July-August surface water phosphorus concentration of 0.040 mg/L. Results of this study suggest that septic tank drainage from recreation areas does not contribute significantly to reservoir phosphorus loading. However, continued urbanization of the upper Henrys Fork basin through recreation homesite development would be expected to increase non-point source phosphorus inflow to the reservoir. The dissolved ortho-phosphorus concentration was exceptionally high (0.602 mg/L) in springs emerging from both developed and undeveloped shoreline areas. Ground-water inflows and bank storage appear to play a dominant role in phosphorus dynamics of the reservoir. Further understanding of ground-water hydrology in the reservoir area and identification of the source of phosphorus in springs emerging from the shoreline would be required to assemble a complete estimate of phosphorus input. Zimmer, D.W. 1981. Bureau of Reclamation, Pacific Northwest Region, Boise ID. 16 pp. plus appendices.