Tiber Reservoir (Lake Elwell) Water Level
Tiber Reservoir (Lake Elwell) is at 2,986.69 ft today (Oct 31), 6.31 ft below its 2,993 ft full pool, down 0.24 ft this week.
Montana · Marias River
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Water level history
About Tiber Reservoir (Lake Elwell)
Tiber Reservoir (Lake Elwell) is a reservoir on the Marias River in Montana, operated by U.S. Bureau of Reclamation. Its full summer pool sits at 2993 ft above sea level. Live water levels come from the U.S. Army Corps of Engineers (CWMS) and update hourly.
Understanding Tiber Reservoir (Lake Elwell)'s water level
Tiber Dam was built to store water for irrigation that never came. The Flood Control Act of 1944 folded it into the Pick-Sloan Missouri Basin Program, and the Guy H. James Company built the zoned earthfill dam on the Marias River between September 1952 and March 1956, about 20 miles southwest of Chester. The plan called for 127,000 irrigated acres, later cut to 89,000 when Lonesome Prairie Valley was dropped. But the dry years of the 1930s had passed, and in 1955 only 42 of 206 resident landowners signed repayment contracts, well short of the 60 percent Montana required. As of 1992 the unit irrigated 3,496 acres. The reservoir left behind, Lake Elwell, is named for Judge Charles B. Elwell, a former director of the Montana Reclamation Association, and spans Liberty and Toole counties.
For its first quarter century Tiber could not be run as designed. By 1957 the foundation materials under the dam's spillway had failed, and Reclamation had to lower the pool every spring. Its daily record shows spring lows in the 2950s and low 2960s through the late 1960s and 1970s, bottoming at 2,953.81 feet in March 1968, well below the 2,966 foot top of inactive storage. The old spillway was diked off and an auxiliary outlet finished in 1969 as a stopgap. The spillway was then torn out and rebuilt with three radial gates between 1977 and 1979, and the dam and its 17,000 foot dike were raised, work accepted as complete in October 1981. Reclamation dates normal operations from that month, and since 1983 the lake has not dropped below 2,973 feet.
The 2,993 foot full pool on this page is the top of the joint use zone, where water held for use and space held for floods overlap. Active conservation storage tops out at 2,976 feet, and exclusive flood control space runs above joint use to 3,012.5 feet. Reclamation's 2021 sediment survey describes a lake that usually swings about 14 feet a year between roughly 2,980 and 2,993, and the record fits: lows come in March and April, the peak arrives with runoff in late June or early July. At full pool the lake covers about 17,900 acres and holds roughly 967,000 acre-feet. That water now has more takers than farms. Chester has piped it since 1962, a 1997 compact gives the Chippewa Cree Tribe of Rocky Boy's 10,000 acre-feet a year, and a treatment plant at the lake feeds the Rocky Boy's/North Central Montana Regional Water System, planned to serve about 43,000 people from the reservation to Havre. A privately owned 7.5 megawatt power plant has run on dam releases since 2004.
Tiber Reservoir (Lake Elwell) — frequently asked
What is full pool at Tiber Reservoir (Lake Elwell)?
2,993 feet, the top of the joint use pool. Below that, the top of active conservation storage is 2,976 feet and the top of inactive storage is about 2,966. Above it, exclusive flood control space reaches 3,012.5 feet and surcharge 3,020.2, with the dam crest at 3,026. At 2,993 the lake spreads over roughly 17,900 acres; at 2,976 it is down to about 13,800.
What is the record high level at Lake Elwell?
3,011.42 feet on 19 July 2011, in Reclamation's daily record going back to 1956. That put the lake about 18 feet over full pool and within roughly a foot of the top of the flood control pool. The next highest years were 1965, which crested at 3,005.59 feet in mid July, and 1964, when the lake reached 3,001.91 feet on 13 June.
What is the lowest Lake Elwell has been?
Leaving aside the first filling in 1956, the low is 2,953.81 feet in March 1968, when a failing spillway foundation forced Reclamation to drain the pool every spring. Since the spillway was rebuilt and the dam raised, the floor has been far higher: the lowest reading since 1983 is 2,973.26 feet in March 1989, and the February 2025 low of 2,977.8 feet was the lowest since 2008.
Why does the lake level change through the year?
Tiber catches the Marias spring runoff and releases it through the rest of the year. The lake is normally lowest in March or April before runoff, then climbs through May and June to peak in late June or early July. Reclamation's sediment survey puts the usual annual swing at about 14 feet, between roughly 2,980 and 2,993. In a big runoff year the lake rises into flood storage above 2,993.
How did Tiber Dam handle the 1964 flood?
In June 1964 the Marias at Shelby peaked near 241,000 cubic feet per second, according to the USGS. Tiber stored most of it. Flow below the dam peaked at about 10,400 cubic feet per second, and Reclamation's record shows the lake rising from 2,973.5 feet on 1 May to 3,001.9 feet on 13 June, a climb of more than 28 feet in six weeks.
What fish live in Lake Elwell?
Montana FWP lists walleye as the most abundant game fish, along with yellow perch, northern pike, rainbow trout, lake trout, burbot, cisco and a small population of shovelnose sturgeon. FWP manages walleye for natural reproduction; the population has sustained itself since stockings in the early 1970s and again in 1986 and 1988. The Pines for Perch project adds spawning cover for forage fish, and FWP lists water levels among the factors that would prompt renewed stocking.
Who gets water from Tiber Reservoir?
Far fewer irrigators than planned: the unit was designed for 127,000 acres but watered 3,496 in 1992. Municipal users matter more. Chester built a pipeline in 1962, the Tiber County Water District draws from an intake tower on the lake, the Chippewa Cree Tribe holds 10,000 acre-feet a year under a 1997 compact, and the Rocky Boy's/North Central Montana Regional Water System treats lake water for communities as far east as Havre.
Other lakes near Tiber Reservoir (Lake Elwell)
- Bighorn LakeMT/WY
- Fort Peck LakeMT
- Canyon Ferry LakeMT
- Lake AshtabulaND
- Boysen ReservoirWY
- Flaming Gorge ReservoirUT/WY
See current levels for all 4 Montana lakes and reservoirs →
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