San Alfonso del Mar is a private resort located in Algarrobo, Chile, about 100 km (60 mi) west of the capital Santiago. It is, according to Guinness world records, the largest swimming pool in the world: 1 kilometre (0.62 mi) long, covering an area of 19 acres (7.7 ha), with a maximum depth of 115 feet (35 m) and holding 66,000,000 US gallons (250,000,000 l; 55,000,000 imp gal) of seawater. The pool, developed by Chilean company Crystal Lagoons, uses water pumped, filtered, and treated from the Pacific Ocean. It has been attracting tourists since it opened in December 2006.
While early estimates put the total cost of construction at about US$ 3.5 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.