The Tri-State Water Quality Council has announced an interstate agreement between Montana and Idaho to reduce pollution flowing into the deep, open waters of Idaho’s Lake Pend Oreille, that state’s largest natural lake, says Council Executive Director Ruth Watkins.
The Border Nutrient Load Agreement, signed by both the director of Montana’s Department of Environmental Quality, Jan Sensibaugh, and her counterpart in Idaho, Steve Allred, solidifies a plan nearly two years in the making to reduce algae levels produced by the nutrients nitrogen and phosphorus.
High levels of these nutrients have been shown to act as “fertilizers” that foster the growth of algae and other plant life in the lake, says Clark Fork Coalition Conservation Director Matt Clifford.
Excessive algae and plant growth can lower the levels of dissolved oxygen in the water, harming fish and other aquatic life.
“Basically, what this means is when the algae dies and decays it depletes the oxygen level,” says Clifford. “This can lead to a fish kill and it can also affect insect life low on the food chain.”
The agreement primarily addresses so-called “nutrient loading” into the Clark Fork River, which provides 90 percent of the lake’s flow and 80 percent of the lake’s load of total nitrogen and phosphorus. Specifically, the agreement focuses on three Montana cities along the Clark Fork: Missoula, Deer Lodge, and Butte, which collectively produce the vast majority of nutrients seeping into the watershed, says Clifford.
“Animal and human waste are a big source of the nitrogen and phosphorus,” he says. “The other main causes are waste from Stone Container, farms and ranches, logging and septic systems.”
In the ’90s, Missoula placed a ban on all detergents with phosphates, which has helped to significantly lower phosphate rates. Currently, the city is combating nutrients by encouraging people with septic systems to hook up to the municipal sewer system. In about a year, the city will begin work upgrading its current sewer system, which will include a nutrient reduction facility.
Both the Council and the Clark Fork Coalition believe this agreement will set a threshold—or water quality target—for the river’s nutrient levels at the Montana-Idaho boarder. The groups are optimistic the targets will provide a framework for future water quality decisions related to any new waste sources that might increase nutrient loading.