The largest pool in the world is San Alfonso del Mar. It is 3,324 ft. long salt water lagoon at the San Alfonso del Mar resort in Algarrobo, Chile. It took 5 years to build and cost about 1.5 billion dollars (US). The pool covers more than 19 acres of surface area, holds 66 million gallons, and has transparent waters down to 105 ft. deep. Maintenance alone amounts to $4 million dollars per year.