Try to find a tour operator to take you midday, after the big morning groups leave and before the afternoon ones come. These lagoons are so salty you can effortlessly float for hours. Make sure to bring lots of fresh water to rinse your eyes and your GoPro off after. There's no shade (welcome to Atacama), so definitely bring a wide-brimmed hat and something light and long sleeved if the desert sun is intense for you...the park gets finicky about visitors applying sunscreen then contaminating the water with it.