There are usually quite a few people on the Plava Laguna from September to April.
From June to September the air temperature at Plava Laguna is perfect for sunbathing. The swimming season at Plava Laguna occurs from July to September, when the water is warm and comfortable for swimming.
In December, in June and in November and October Plava Laguna has rainy season. This is something to keep in mind when planning your trip since it is quite possible that you may be unable to sunbathe.