September 21, 2006
In August, water quality in the Clark Fork River below Milltown dam was monitored daily for turbidity (the “cloudiness” of the water), and weekly for suspended sediment, metals, and arsenic. Upstream sites on the Blackfoot River and on the Clark Fork at Turah were also monitored weekly for metals, arsenic, and sediment. The reservoir level was not lowered during the month – the drawdown that began June 1 remained between 8.5 and 9 feet, depending on river flows.
Turbidity and sediment levels below Milltown Dam remained low, along with very low river flows throughout the month. Levels of dissolved metals and arsenic were also low and typical of the levels usually seen in the river at this time of year. All parameters were well below the applicable water quality standards.
Montana Fish, Wildlife & Parks monitored the condition caged fish in six locations in the Blackfoot, Clark Fork and Bitterroot Rivers between July 11 and August 4. Because of very high stream temperatures, agency biologists saw a tremendous amount of mortality, and this appeared to be related to high water temperature and the resulting low dissolved oxygen (caused by high temperatures). The Bitterroot River near the mouth and the Alberton location had the highest water temperatures and lowest dissolved oxygen, and 100% of the caged fish died in these locations. Typically, the Milltown site had the highest dissolved oxygen. Death rates of caged fish in the Blackfoot, on the Clark Fork at Turah (above the dam) and at Milltown (below the dam) were similar – up to a quarter of the caged fish died in these locations.
FWP is also tracking wild fish by radio telemetry on a weekly basis, and during this period saw no major movement and no mortality. The caged fish experiments will be deployed again this September at the 5 locations (Turah, Blackfoot, Milltown, Bitterroot, and Alberton) once the drawdown resumes. FWP will monitor these changes through February- similar to last year.
And a reminder: if you see one of the cages, please don’t disturb it. These cages supply critical information for monitoring effects of the Milltown project.