The Ostional Wildlife Refuge protects marine turtle species, such as the Olive Ridley (Lora) and Leatherback (Baula) at Playa Ostional. Arrival of these species at this beach is considered the largest in the world, with as many as a million sea turtle eggs laid in the beach nesting areas each year.

Some days or weeks before an expected "arribada", you can see an increasing number of turtles swimming close offshore. This is then the gathering of this particular group of turtles that will be taking part in the next event. As an individual will nest between four and six times a year, there will probably be females present that nested in the previous "arribada".