Thousands of Olive Ridley Turtles Come Ashore in One of the Year’s Largest Arribadas

One of the largest arribadas of the year began in the early morning hours this morning at the Ostional National Wildlife Refuge in Guanacaste, as thousands of olive ridley sea turtles emerged from the Pacific to nest on the beach long known as their favorite stretch of Costa Rican coastline.

Guides and residents alike described this week’s event as among the biggest seen so far in 2026. More turtles were expected to continue arriving through Friday night and into Saturday morning. The spectacle draws both Costa Ricans and tourists eager to watch the turtles come ashore, dig their nests, lay their eggs and return to the sea. That cycle has made Ostional one of the most closely watched nesting sites in the world.

The timing fits a well-established seasonal pattern as well as arribadas occur throughout the year at Ostional, but September, October and November typically bring the largest events, when more than 100,000 turtles can come ashore in a single night and a single arribada can stretch on for up to two weeks.

Dry season arribadas, running roughly from January through July, are considerably smaller. Those events usually bring fewer than 20,000 turtles over three or four nights. Friday’s event also arrived on schedule as arribadas at Ostional cluster around the last quarter moon, which fell on September 4, and can begin two days before or after that phase.

The refuge is patrolled daily by park guards who track nesting activity along the beach. When the number of turtles climbs to around 1,000 in a given arribada, the Asociación de Desarrollo Integral de Ostional, the local community development association, can declare what is known as an arribada aprovechable.

That designation sets several things in motion at once. It triggers Costa Rica’s official monitoring operation and allows members of the local community to carry out a legal, regulated harvest of a portion of the eggs. It also closes the beach to anyone not accompanied by a certified local guide, with groups capped at nine visitors.

The guide rule is not a formality but a nesting female that is startled will abandon the attempt and return to the water without laying, and a beach at this density is packed with fresh nests that are easily crushed underfoot. Flash photography and white flashlights are prohibited for the same reason.

The harvest itself is limited to the first days of an arribada, when eggs laid early are likely to be dug up and destroyed by the waves of females arriving behind them. The model has operated at Ostional for more than three decades and remains one of the only sites in the world where a regulated harvest of sea turtle eggs is permitted.

The refuge covers 468 hectares (1,156 acres) of land and 8,000 hectares (19,768 acres) of ocean along 16 kilometers (10 miles) of coast, taking in not only Ostional but also the beaches of Nosara, Pelada and Guiones. Final turtle counts and nest totals for this week’s arribada were not yet available. Those figures are typically released by Costa Rican wildlife authorities and the local association once monitoring concludes, generally a few days after the largest nightly arrivals taper off.

Anyone planning to travel to Ostional in the coming days should confirm tour availability with the local guide association before setting out. Access during an arribada is by guided group only, and slots fill quickly when a large event is underway.

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