Lake Monroe, the largest lake in Indiana, is the primary water supply for Bloomington and the surrounding areas. It is a major recreational attraction, boasting several marinas, state recreational areas, and beaches. Covering parts of three counties, the lake was begun in the 1960's by the Army Corps of Engineers and completed in 1970.
Originally designed for flood control, Lake Monroe was authorized by Congress in 1938, but it wasn't until 1960 that construction began with the Army Corps of Engineers damming Salt Creek roughly ten miles southeast of Bloomington. Prior to construction, there existed several small communities in the valley, including the small town of Elkinsville. Most of the residents were made to leave if their property fell below a certain elevation. Construction of the dam was completed in 1965.
The lake is 10,760 acres. A map lists 23,962 acres as the area around the lake. It is located across 3 counties. At its deepest, just in front of the dam in the Salt Creek channel, Lake Monroe is roughly 54 feet deep at normal pool with an average depth of 25 feet. The water level is regulated by the Corps of Engineers and is relatively stable, but may fluctuate up to 18 feet depending on storage needs. The dam is located at the southern end of the lake, which provides one of the most popular boat mooring locations. The eastern part of the lake, separated by the SR 446 causeway is much more shallow (ranging from 20-30 feet near the causeway to as low as three feet near the Pine Grove boat ramp) and has idle zone restrictions throughout. There are many inlets that provide protection against the waves. On weekends, these are typically packed with large boats and waverunners tied together in long lines.
The lake is open for recreational boat use and there are several Marinas that provide year-round boat docking. The largest Marina is the Fourwinds Resort & Marina accessible via the Fairfax entrance to the lake. There are several boat launches at various points throughout the lake. Some have criticized the usage of motorized boats on the lake since it supplies most of the county's drinking water.
There are several parks and small beaches that are popular in the summer. The largest beach is the Fairfax beach on the western side of the lake. Slightly smaller is the Paynetown beach accessible from SR 446. Both locations provide covered and open picnic tables as well as restroom facilities. The recreational facilities are operated by the Department of Natural Resources. There is a small charge per vehicle to gain admission to the recreational areas, though some boat ramps do not carry fees.
Given the lake's location in the Hoosier National Forest there are a number of trails that open out onto the lake.
The reservoir provides the majority of water for Monroe County, though it has been deemed inadequate in recent years. Some have criticized the allowance of motorized vehicles on the lake as well as some of the development projects along the shores, citing concerns over the quality of the water supply.
A 1964 study concluded that Lake Monroe, from the top of its conservation pool at elevation 538.0 to elevation 525.75, could safely provide a uniform flow of 47 million gallons per day (mgd) for one year without any runoff being re-supplied to the lake. The firm yield of Lake Monroe was conservatively estimated to be 50 percent more than the 47 mgd, or approximately 70 mgd. Another, later study concluded that the lake could potentially produce 122 mgd, but this figure seems unreasonably high: the yield was based only on direct withdrawals which was then further separated into direct withdrawals (30 mgd) and downstream uses (92 mgd)(1). The lake was built to have a 100 year lifespan and thus should be capable of providing water to Monroe County through 2066.