| Abstract/Description or Keywords |
Downton Lake Reservoir is a large glacier-fed hydroelectric reservoir in southwestern British Columbia. Following a brief investigation of this reservoir at drawdown, in May 1996, a broader assessment of fish and fish habitat within the drainage was conducted during October 7-26, 1996. This was complimented by an associated study, monitoring limnological conditions in the reservoir itself, from fall 1996 to summer 1997. Throughout the October 1996 field investigations, the reservoir was close to full pool. Streamflows were low, as usual for that time of year. Rainbow trout was the only fish species captured anywhere in the drainage, during these investigations. The majority of sampling effort was expended on an evaluation of habitat and associated populations of fish in tributary streams, above full pool. Generally speaking, spawning habitat appeared to be limited and/or inaccessible in most streams. In addition to the predominantly small and steep tributaries along the north and south sides of the reservoir, this also applied to the upper Bridge River, a moderately large system, and predecessor to the reservoir itself. In sampling of the upper Bridge River system, rainbow fry were only captured in a discrete network of side channels approximately 2.5 km upstream of the reservoir, at full pool. In addition to superior spawning substrates, these channels also offered clear flows and warmer temperatures, compared to the highly turbid and cold waters of the Bridge River rnainstem, and McParlon Creek, a major tributary to it. In the numerous smaller tributaries to the reservoir, steep gradient and/or specific barriers to fish passage frequently limit ( or preclude) access to streamlength above the full pool level. Other than the Bridge River side channels noted above, only one other stream section (in a smaller tributary to the reservoir) was found-to contain significant numbers of fry. |
