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USGS Water-Year Summary 2024
13126000 MACKAY RESERVOIR NEAR MACKAY, ID
LOCATION - Lat 43°57'05", long 113°40'30" referenced to North American Datum of 1983, in NE 1/4 SW 1/4 sec.12, T.7 N., R.23 E., Custer County, ID, Hydrologic Unit 17040218, Mackay Reservoir quad., on gate-control tower of Mackay Dam on Big Lost River, and 4 mi northwest of Mackay.
DRAINAGE AREA - 797 mi².
SURFACE-WATER RECORDS
PERIOD OF RECORD - January 1919 to current year.
GAGE - Water-stage recorder. Datum of gage is 6,004.63 feet above NAVD 1988. Prior to Oct. 15, 1959, non-recording gage at same site and datum.
REMARKS - Reservoir is formed by earth and rock-fill dam, which was reconstructed in 1917-18; storage impounded by original dam not recorded. Crest of spillway was raised 5 ft. in September 1956. Capacity is 44,370 acre-ft. between gage heights 7.0 and 66.5 ft., crest of spillway. Dead storage reported to be about 125 acre-ft. Water is used for irrigation of about 33,000 acres in Big Lost River irrigation district. About 12,700 acres irrigated from Big Lost River and tributaries above reservoir by surface diversions, and about 10,200 acres irrigated by sub irrigation. Considerable seepage around dam because of its porous foundation, but the greater part of this water returns to Big Lost River between reservoir and station below reservoir, near Mackay. Prior to Oct. 1, 1959, contents below 1,000 acre-ft. may be in error at times, as readings at the gage were too low because of fall in the outlet channel. Figures given herein represent usable contents.
EXTREMES FOR PERIOD OF RECORD - Maximum contents, 46,100 acre-ft May 14, 1976, gage height, 67.73 ft; no available contents during periods in 1919-20, 1924, 1926, 1929, 1931-35, 1974; minimum gage height observed, 6.3 ft, Aug. 5, 1934.
