San Alfonso Del Mar Pool And Resort, Algarrobo, Chile

San Alfonso's pool is 1 kilometre (3/5 mile) long. The pool covers an area of 7.7 hectares (19 acres) that holds 250 million liters (66 million gallons) of seawater. The pool, developed by Chilean company Crystal Lagoons, uses water pumped, filtered, and treated from the Pacific Ocean to supply to the pool.
Development
While early estimates put the total cost of construction at about US$ 3.5 million (€2.8 million) for the pool alone, more recent, and perhaps accurate estimates are in the area of $1.5 to 2 billion USD total for construction and almost $4 million USD in annual maintenance.