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Location.--Lat 47º41'50", long 114º09'37", in SW 1/4 SE 1/4 NE 1/4, sec 4, T.22N.,R.20W., at south end of Flathead Lake, at Polson, Lake County. Hydrologic Unit 17010208.
Drainage Area.--7,086 mi²
History.--Apr 24, to Aug. 5, 1900, daily lake elevations only at site near Holt, 6 miles east of Somers (Datum unknown)
Published record at Polson gage: Aug 1908 to June 1909 (fragmentary record), Jan. 1910 to Dec. 12, 1926, June 1928 to Sept. 30, 1941 and Oct. 1, 1998 to current year.
Published record at Somers gage: Apr. 1923 to Sept. 30, 1998
On August 3, 1998 the Flathead Lake at Somers, MT (12371500) gage was removed and the gage at Polson became the only USGS gage on the lake. Unpublished daily lake elevations at Polson 1941-1998 are available in files of the Helena District office.
Zero gage datum for both the Polson and Somers gages is 2,800 ft. Somers Datum (NGVD 29, Subtract 1 foot to convert Somers Datum to Sea Level). August 1908 to September 30, 1921, data were obtained from a staff gage on the steamboat pier at Polson 150 ft. west at a datum of 2,803.00. ft. above mean sea level (Somers Datum).
Regulation and Diversions.--The lake elevation between 2,883 and 2,893 feet Somers Datum is subject to regulation by Kerr Dam since April 1938. Kerr Dam is operated by PPL Montana, LLC and is located about four miles below the lake outlet at Polson.
Many small diversions on tributary inflow to the lake. South Fork Flathead River tributary inflow is regulated by Hungry Horse Dam since September 21, 1951.
Cooperation.--Federal Power Commission, Project No. 5.