The Ostional National Wildlife Refuge was established in 1983 with the primary mission as the conservation of sea turtles and the protection of their reproductive habitat. The Refuge extends 15 km along the shoreline, including the beaches of Ostional, Nosara, Pelada, and Guiones on the Guanacaste peninsula. It covers 200 m of coastline, also extending inland along estuaries and mangroves and including 3 nautical miles of marine protected area.
Ostional is one of the most important sites for the olive ridley sea turtle in the world, second only to Escobilla, Mexico. This site is one of few in the world to host the mass-nesting behavior, known as arribadas, a phenomenon considered one of the most amazing wonders of nature. During arribadas, tens and sometimes hundreds of thousands of sea turtles come ashore to nest simultaneously over a period of several days. Ostional hosts the highest frequency of mass-nesting events and densest concentration of olive ridley sea turtles on Earth.
Additionally, the Ostional National Wildlife Refuge protects important habitat for a diversity of coastal and marine flora and fauna, including mangrove and rocky intertidal ecosystems, with connectivity through the Rio Nosara Biological Corridor to Parque Nacional Barra Honda and Parque Nacional Diría.
