July 6, 2006
Monitoring of caged fish by the Fish, Wildlife and Parks Dept. has shown significant mortality, causing the EPA to halt the drawdown of the Milltown Reservoir. Caged fish below the Milltown Dam have shown 100 percent mortality. And why that happened is still a mystery, though agency officials believe it may be linked to high temperatures of late. And until those temperatures drop, the EPA has halted the drawdown, which is now at more than nine feet.
For more on the fish kill, see the Missoulian coverage or the EPA media advisory below:
Helena, Montana —
The draw down at the Milltown Reservoir which began on June 1, 2006 has been proceeding as planned and the water level has now dropped more than nine feet. EPA and Montana Department of Environmental Quality are working with their partners (Envirocon, Missoula County, the University of Montana, the US Geological Survey, and the Montana Department of Fish, Wildlife and Parks) to monitor fish health, surface water, and groundwater during the draw down. The monitoring plan is in place and working as envisioned.
To monitor fish health, Montana Fish, Wildlife and Parks has set up cages of fingerling rainbow trout above and below the Milltown Dam. In addition, free roaming fish have been tagged with radios to monitor movement and their survival. The caged fish are very sensitive and serve as an early warning system, alerting authorities to possible stresses on fish. Recently, there have been an increased number of fish mortalities in these cages even though the metals, turbidity, and total suspended solids readings have been low. During the past week, there has been 100% mortality of the caged fish in the Clark Fork River below the Milltown Dam and in the Clark Fork River below the confluence with the Bitterroot River. Comparatively, approximately 23% mortality was seen this year in the control stations in the Blackfoot River, Bitterroot River and Clark Fork River above the dam, and less than 10% mortality at the Clark Fork sites in 2005 when there was no drawdown. Free roaming fish have also had unusually high mortality, corroborating the results of the caged fish.
Not all the information has been collected and analyzed to understand the mechanisms for this mortality. Results are preliminary and should be interpreted with caution.
Recent and predicted continued high temperatures are adding stress to all fish in the river. Therefore, EPA, in consultation with Montana DEQ and Fish, Wildlife and Parks, will maintain the current water level until river water temperatures drop and the fish are less stressed.
The monitoring system is working and EPA and FWP are taking the necessary steps to protect aquatic life and ensure a healthy, productive fishery in the Clark Fork River.
To date, the surface water monitoring results have been low, much less than was predicted for total suspended solids, dissolved metals, and volume of material scoured from the reservoir. In fact, the dissolved metals detected below the dam were transported from upstream of the reservoir.
A network of monitoring wells has been set up as part of the ground water monitoring program. Missoula County, with funding from EPA, is monitoring the water levels in area wells. EPA has paid for replacement of 10 wells at risk of going dry as the draw down proceeds. Missoula County, again with funding from EPA, has free test kits for residents who want to test their wells for arsenic.
The Milltown Reservoir cleanup project is on schedule with work on the bridges< over the Blackfoot River planned for this fall and removal of the Milltown Dam planned for spring 2008.
The Milltown Reservoir draw down signaled the start of Phase I of the Remedial Action and cleanup activities for the Milltown Dam. The draw down is permanent and necessary for a number of reasons: 1) Allow additional site exploration to help in design; 2) Allow precautionary stabilization work on the I-90 and Highway 200 bridges crossing the Blackfoot River; and 3) Set the stage for other needed site work this fall.
For additional information about the Milltown Project, please visit the following websites:
Site-related design documents: