Lake Texoma is one of the largest reservoirs in the United States, the 12th-largest US Army Corps of Engineers' (USACE) lake, and the largest in USACE Tulsa District. Lake Texoma is formed by Denison Dam on the Red River in Bryan County, Oklahoma, and Grayson County, Texas, about upstream from the mouth of the river. It is located at the confluence of the Red and Washita Rivers. The project was completed in 1944. The damsite is about northwest of Denison, Texas, and southwest of Durant, Oklahoma. Lake Texoma is the most developed and most popular lake within the USACE Tulsa District, attracting around 6 million visitors a year. Oklahoma has more of the lake within its boundaries than Texas. Hydrology Tributaries and outlet Lake Texoma's two main sources are the Red River from the west and Washita River from the north. Other notable sources include Big Mineral Creek, Little Mineral Creek, Buncombe Creek, Rock Creek, and Glasses Creek. Lake Texoma drains into the Red River at the Denison Dam. Water levels Normal elevation of the conservation pool varies from National Geodetic Vertical Datum depending on the time of year. The flood control pool extends to elevation . The lake has crested the dam's spillway at a height of five times - once in 1957, 1990, and 2007, and on May 24 and June 18, 2015. (USACE 2003a) The lake's previously highest elevation was recorded on May 6, 1990, at 644.76 feet. This record was broken on May 29, 2015, and the lake crested on June 1, 2015, at a new record elevation of 645.72 feet. The top of Denison Dam is at 670 feet. Saltwater from the Red River The Red River that formed Lake Texoma is a saltwater river due to salt deposits left over from a 250-million-year-old former sea that was in the current Texas-Oklahoma border region. As time passed, that sea evaporated, leaving salts deposits — mostly sodium chloride. Rock and silt eventually buried the deposits, but the salts continue to leach through natural seeps in tributaries above Lake Texoma, sending as much as 3,450 tons of salt per day flowing down the Red River. The problem with the water in the Red River is much of it is too salty and requires costly treatment, if it is usable at all. Due to this phenomenon, striped bass, a saltwater fish species, thrives in Lake Texoma. Lake Texoma