Flathead Lake is a natural freshwater lake. However, the top ten feet of the lake are regulated by privately owned, federally licensed Kerr Dam, located on the Flathead River approximately four miles below the outlet of the lake at Polson. Completed in the spring of 1938, Kerr Dam is now owned by PPL Montana, and can generate up to 194 megawatts of electricity.
The construction of Kerr Dam, and of Hungry Horse Dam on the South Fork Flathead River, completed in 1951, led to expectations of predictable lake levels and opportunities to maintain elevated lake levels for summer recreation. A Memorandum of Understanding between the power company and the Army Corps of Engineers determined that, barring potential flooding, the lake level should reach 2890 feet Somers Datum (SD)* by May 30 and 2893 feet (considered the “full pool” lake leve) by June 15 for summer recreation. Since the dam operator is required to prevent the lake level from exceeding 2893 feet, the “operational full pool” level is a couple inches below 2893.
Kerr Dam’s 50-year license was renewed in 1990. The relicensing process included a series of reviews and studies that resulted in new license requirements for mitigating the dam’s impacts and managing the dam’s operations, including requiring a new Drought Management Plan. The new license also provides the Confederated Salish & Kootenai Tribes the option of purchasing the dam in 2015.
The operation of the dam, which is an element of the Columbia River Basin hydropower system, is governed not only by the license, but by flood control and fisheries requirements, and by various agreements, and involves many federal, state, and local agencies.
Since Kerr Dam was built, severe droughts occurred in 1941, 1944, 1977, and 2001. During the most recent drought, in 2001, the lake level dropped below 2892 feet for most of the summer. Public concerns spurred action to develop the drought management plan required by the Kerr Dam license, which had yet to be produced.
Major floods that raised the lake level above 2893 feet up to 2896 feet occurred frequently before Hungry Horse Dam impounded the South Fork Flathead River. The most notable of these floods occurred in 1913, 1916, 1927, 1928, 1933, and 1948. The great flood of June, 1964, which inundated thousands of acres of the Flathead Valley, raised the lake level to just over 2894 feet for a couple of days. There has been no other significant excursion above 2893 feet since Hungry Horse Dam was completed in 1951.
For more information, please visit the links on the menu on the left of this page. As we continue to update this section of our website, we are maintaining links to graphs and other lake level information from our old website. To view this information, go to LINK.
*What does Somers Datum mean?
Somers Datum (SD) is the reference elevation for the USGS’s lake level measuring gauge at Polson. The datum is called the “Somers Datum” because the gauging station was previously located near Somers, but was moved to the Polson location in 1998. Converting SD elevations to mean sea level or to elevations referenced to different datums requires applying a correction factor.
Before and after Kerr Dam mean annual lake levels