Water Quality

Water quality in Flathead Lake

Flathead Lake is an outstanding aquatic resource. The lake remains among the cleanest large lakes in temperate regions worldwide. But research shows that water quality in Flathead Lake has been declining since the 1970s. Primary productivity, or the rate of algae growth, is increasing according to Flathead Lake Biological Station Director Dr. Jack Stanford. And the amount of dissolved oxygen in water at the bottom of Big Arm Bay is declining. These two trends are indications of declining water quality.

Phosphorus and nitrogen are nutrients that contribute to algae growth. Past efforts to reduce the amount of nutrients reaching Flathead Lake and its tributaries have been successful. Upgrading sewage treatment plants in the upper basin for phosphorus removal, hooking up Evergreen (an unincorporated semi-urban area) to the Kalispell sewer system, and banning phosphorus-containing detergents have reduced the amount of nutrients reaching Flathead Lake from these sources. However, water quality continues to be threatened by nutrient pollution from runoff.

Clean water's biggest threat:  Polluted runoff

Polluted runoff, also known as nonpoint source pollution, is our leading threat to water quality. It is caused by rainfall or snowmelt moving over and through the ground. As it moves, runoff picks up and carries natural and human-caused pollutants, finally depositing them into rivers, lakes and groundwater.

Croplands, livestock feedlots, golf courses, lawns, gardens, roadways, parking lots, construction sites, landfills, city storm drains, logging operations, residential septic systems, and erosion from streams, river banks and lake shores are all sources of polluted runoff. Even airborne chemicals and particulates carried into our waters by rain or snow contribute to the problem.

The scattered locations of these pollutants and their often unpredictable dispersal make clean up efforts complex and often costly. This is because the waterways within a watershed are interconnected – streams flow into rivers, which flow into lakes. And there can be a connection between these surface waters and groundwater. A pollutant introduced in one area upstream can pollute the water downstream.

Major sources of polluted runoff

Farms and cities rank as the major sources of polluted runoff, according to the Environmental Protection Agency (EPA). Studies by the University of Montana Flathead Lake Biological Station confirm this. They have found that the valley area north of Flathead Lake is contributing a large share of the polluted runoff that eventually reaches Flathead Lake.

Pollutants from agriculture can include pesticides, nutrients from fertilizers, sediment form soil erosion, and bacteria and nutrients from manure.

Pollutants come from urban and suburban areas through the use of pesticides and fertilizers in maintaining lawns and gardens. Streets and parking lots accumulate gasoline, lead, oil, and grease from automobiles, contributing to polluted runoff following heavy rains.

Who is responsible?

The solution lies in the prevention of pollution through the collective responsibility of individuals, governments, and corporations. If each group and family takes responsibility for the lands they manage and the pollution they generate, polluted runoff can be greatly reduced.

When the land is covered with crops, shrubs and trees, these plants take up and use nutrients, keeping them from reaching the groundwater, streams, and eventually Flathead Lake.

Preventing pollution is the sensible course. Everyone has an important role.

Montana lists Flathead Lake as impaired water body

Flathead Lake has been listed as an impaired water body by the Montana Department of Environmental Quality (DEQ) since 1996. Consequently, Total Maximum Daily Loads (TMDL), or the maximum amount of pollutants that may be present in the water and still meet water quality standards, were determined for Flathead Lake to guide restoration efforts to reduce excess nutrients reaching the lake.

DEQ completed a Nutrient Management Plan and Total Maximum Daily Load for Flathead Lake report in 2001, as required for impaired water bodies by the federal Clean Water Act. The plan sets various water quality targets, including a 15% reduction in nitrogen and phosphorus loads.

Water Quality Monitoring

Monitoring water quality in Flathead Lake and its tributaries is vital for understanding long-term trends. Only then can we understand whether water quality is getting worse or better and take appropriate actions. Monitoring is also important to evaluate the effectiveness of protection and restoration activities to reduce pollution. For more information about the Flathead Basin Water Quality Monitoring Program conducted by the University of Montana Flathead Lake Biological Station, see Monitoring: The Key to Understanding and Protecting Flathead Lake. There is also a volunteer lake monitoring program:  Northwest Montana Lakes Volunteer Monitoring Network.

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