Hot summertime weather has led to low flows and reservoir levels in the Northwest.
The Hebgen Lake Reservoir in Southwest Montana dropped below its minimum summer elevation on July 22 and will remain so for the rest of summer, NorthWestern Energy spokeswoman Jo Dee Black told Water Power West.
Dry, hot weather has required NorthWestern to spill water from the already low reservoir in an effort to cool temperatures in the Madison River, home to rainbow and brown trout and other fish species.
The spill hasn't affected the company's Madison hydroelectric plant, which is undergoing a three-year upgrade that will increase its peak capacity from 8 MW to 12 MW when it is back on line in 2022.
Avista on July 30 said it had started discharging the 500 cfs minimum flow from its Post Falls hydropower development—specified under its FERC license—to help maintain Coeur d'Alene Lake levels, as well as to keep water in the Spokane River throughout the summer.
The action stems from continued hot and dry weather that has reduced the lake's water levels and flows in the Spokane River, which drains the northern part of the lake. During the summer, Avista is required to release at least 600 cfs from the Post Falls development at all times, unless the elevation of the lake drops more than 3 inches below summer level.