Balmorhea State Park

Balmorhea State Park is built around San Solomon Springs, one of the most productive artesian springs in Texas, which has discharged millions of litres of crystal-clear water at a constant 26°C for thousands of years. The park's concrete swimming pool — one of the world's largest spring-fed swimming pools at nearly 2 acres — was built by the Civilian Conservation Corps in the 1930s in the heart of the Chihuahuan Desert. The spring supports a unique aquatic ecosystem including the Comanche Springs pupfish, an endangered species endemic to the area.