This is amazing from Google Sight Seeing:
Apparently officially recognised by the Guinness Book of World Records, here in San Alfonso del Mar in Chile you can hardly miss the world’s largest swimming pool! This absolutely immense pool is 1 kilometre long and covers eight hectares – that’s 80,000 square metres! Furthermore, it contains an incredible 250,000 cubic metres of water. And yes, it’s right beside the beach, and no more than a stone’s throw… from the sea.
Original page is here.