Balmorhea State Park, Natural spring swimming pool in Reeves County, US.

Balmorhea State Park is a natural park in Reeves County, West Texas, built around a natural spring. The swimming pool is fed by San Solomon Springs and stays between 22 and 24 degrees Celsius year-round.

The Texas State Parks Board bought San Solomon Springs and the surrounding land in 1934. Company 1856 of the Civilian Conservation Corps built the pool between 1934 and 1941 under New Deal programs, along with the bathhouse, residences and the San Solomon Springs Courts motel units. A private concessionaire ran the facility until 1968, when the Parks and Wildlife Department took over and it joined the state park system.

The springs were once called Mescalero Springs after the Apache groups who long used this water source in the Chihuahua Desert. Today families from across West Texas drive here to swim in one of the few permanent bodies of water in an otherwise dry region.

The park caps daily entry at 900 people, so come early in the morning during busy periods. The pool bottom is flat in the shallower areas and natural rock in the deeper ones, reaching 30 feet (9.1 m) at its deepest. The water stays between 72 and 76 °F (22–24 °C) all year.

The spring releases between 83 and 106 million liters of water daily, so the pool never needs chlorine treatment. Some of the fish living in the pool are descendants of species that have been in these waters for thousands of years.