1997 Lake Tapps Survey: The Warmwater Fish Community of a Reservoir Managed for Hydropower

Lake Tapps is a large reservoir (1,125 hectares at full capacity) which was created by flooding four smaller lakes with water diverted from the White River during the early 1900's. Numerous islands and peninsulas were formed, resulting in a complex, extended shoreline [length = 67.6 kilometers (km)]. The mean depth in Lake Tapps is 7.6 meters (m), whereas the maximum depth is 27.4 m. Given the colloidal nature of the lake, due to glacial silt from the White River, light penetration is low, resulting in low to moderate primary productivity and few, if any, aquatic plants.

Development on the lake is moderately high (average number of nearshore homes exceeds 8/km shoreline). There are 10 private neighborhood parks, and one private campground maintained by Puget Sound Energy (PSE). Public access includes the Lake Tapps County Park (Pierce County) at the north end of the lake, and the City of Bonney Lake’s Allen York Park at the south end. Recreational activities include fishing, water skiing, jet skiing, and other small water-craft use.

Lake Tapps has been managed for hydropower generation for most of the 20 century. The lake th experiences annual fluctuations in depth (‘drawdowns’) of up to 8.5 m, which undoubtedly contributes to the paucity of aquatic vegetation. Maximum drawdown occurs during late winter or early spring (elevation ~ 157 m). However, during peak recreational months (summer), the lake is maintained at full pool, or an elevation of 166 m. Hydraulic residence time at mean flow (949 cfs) is about 36 days. At maximum flow (2,000 cfs), hydraulic residence time decreases to about 17 days (PSPLC 1983). The short residence time and reduced light penetration probably account for the low to moderate primary productivity in the lake.

In 1990, the Washington Department of Fish and Wildlife (WDFW), then Washington Department of Wildlife, and PSE, then Puget Sound Power & Light Company (PSPLC), agreed to develop a resident fisheries enhancement plan for the reservoir. The Lake Tapps fisheries enhancement plan was developed as a condition for the Federal Energy Regulatory Commission (FERC) hydropower license. The license was issued on December 17, 1997, and has been appealed by several parties. Currently, the resident fisheries enhancement plan is under abeyance pending the status of the license issued to PSE by the FERC to operate the hydroelectric project at Lake Tapps. The plan includes a salmonid stocking program, warmwater fish habitat improvements, and follow-up studies by both organizations to monitor the success of these efforts. The first aspect consists of a plan to stock thousands of kokanee (Oncorhynchus nerka) fry and fingerling rainbow trout (O. mykiss) into the lake, whereas the second consists of a plan to deploy several artificial reef structures along the 7.6 m depth contour at locations selected by WDFW. Still, no recent information exists regarding the resident fish community at the lake. Therefore, in an effort to assess the warmwater fishery at the lake, especially given the warmwater fish component of the enhancement plan, personnel from WDFW’s Warmwater Enhancement Program conducted a fisheries survey at Lake Tapps in fall 1997.