2023 State of the Lake Report

2023 State of the Lake Report

Flathead Lake Continues to be the Shining Jewel in the Crown of the Continent

Since 1977, the Flathead Monitoring Program at the Flathead Lake Biological Station has used standardized scientific methods to collect fundamental physical, chemical, and biological data on Flathead Lake and its main inflows. To assess water quality, FLBS scientists can assess water quality by analyzing key monitoring variables. These variables include water clarity, abundance of planktonic algae, oxygen levels in the lake’s bottom waters, and the supply of key nutrients, especially phosphorus (P), that can drive increases in algae that degrade water clarity and deplete deep water oxygen.

To collect data in these areas, the FLBS Flathead Monitoring Program conducts year-round sampling at a fixed sampling site called Midlake Deep, which is the lake’s deepest point and is located near the Bio Station. Recently, FLBS scientists assembled a report to analyze 2023 sampling data and put it into a greater historical context.



The scientists found that the state of Flathead Lake in 2023 was excellent. In all four of the parameters there were no signs of long-term or even recent deterioration of the lake’s world-class water quality. This continued status indicates that our community’s measures to protect the Flathead Watershed and to reduce nutrient inputs via wastewater treatment have been effective. Data for 2023 are consistent with these long-term observations, despite the drought conditions, low river inflows, and low summer lake level that occurred.

This report represents how special our beloved Flathead Lake truly is, as most freshwater lakes around the world are showing signs of water quality decline. It also demonstrates that the continued vigilance, hard work, and investment from local communities, residents, organizations, agencies, businesses, and more is making a difference in the present and for the future of our waters. A deep and heartfelt thank you to everyone out there working tirelessly to keep our waters clean and blue for generations to come!

See the full 2023 State of the Lake Report