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Phosphorus Alliance

September 5, 2018

Flathead lake, Montana

Flathead Lake in Montana is the largest natural freshwater lake in the western continental US (by surface area). It is also one of the cleanest large lakes in the world, with amazingly transparent water attracting people for fishing, swimming and water sports. The lake is a vital part of the Crown of the Continent, the largest intact ecosystem in the United States.

The health of the lake owes a lot to the Flathead Lake Biological Station (FLBS), which has conducted a scientifically-rigorous monitoring program since 1977. On August 1, 2018, the FLBS was presented the prestigious Stewardship Award by a local lake protection group, the Flathead Lakers. The Stewardship Award was given in recognition of the Bio Station's sustained and outstanding contributions to the protection of Flathead Lake and its watershed.

By all historical reports Flathead Lake was highly oligotrophic, meaning lacking in key nutrients such as phosphorus and nitrogen, a condition reflecting the largely undeveloped nature of its watershed in wilderness and national park. However, during the 1970’s, FLBS monitoring indicated higher levels of nutrients and algae growth due to population expansion that resulted in untreated sewage entering the lake. During this time, FLBS itself installed a modern wastewater treatment plant to treat its own sewage, a plant with advanced phosphorus removal capacities that were cutting edge at the time. Following this successful local demonstration, this technology was soon adopted by local communities such as the city of Kalispell. During subsequent years, FLBS monitoring has documented that levels of phosphorus loading to the lake as well as phosphorus concentrations in the lake have actually declined. As a result, the lake has maintained its world-famous water clarity.

However, new concerns have arisen, especially surrounding the impacts of aging and improperly installed septic tank systems associated with the lake’s growing population. In response, new distributed household and neighborhood treatment systems are likely needed to maintain the health and cleanliness of Flathead Lake. Indeed, FLBS itself needs to replace its now outdated wastewater treatment plant and seeks to implement a modular resource recovery system that will recycle phosphorus and nitrogen and capture bioenergy.

Flathead Lake is a success story in a time when about 40 percent of rivers and lakes in the U.S. surveyed by the EPA are too polluted for swimming or fishing, and lakes across the US are impacted by harmful algal blooms. The FLBS’s experience demonstrates the importance of ongoing vigilant monitoring that is connected to an engaged community in maintaining a lake’s health and cleanliness.

Dr. Jim Elser is executive director of the Sustainable Phosphorus Alliance and director of the Flathead Lake Biological Station. Read more about the FLBS and the Stewardship Award at https://flbs.umt.edu/newflbs/outreach/news-blog/posts/flbs-receives-stewtardship-award/