Costa Rica will reduce visitor capacity at the Sirena Biological Station in Corcovado National Park after technical inspections found serious problems with the station’s wastewater treatment system. The Osa Conservation Area, known as ACOSA, announced the reduction as a preventive measure aimed at lowering the wastewater load entering the system and preventing further environmental damage inside one of Costa Rica’s most important protected areas.
Sirena is one of the main access points for visitors to Corcovado, a park known for its wildlife, remote trails, and high concentration of biodiversity. The station receives both day visitors and overnight guests, making it one of the most heavily used areas inside the park.
The wastewater treatment plant at Sirena began operating in 2016 as part of the BID Tourism Project. The system was designed to serve about 100 people per day. Since 2022, however, the plant has regularly handled wastewater loads linked to more than 200 daily users, placing pressure on a system that authorities say is no longer operating under acceptable conditions.
A November 2025 inspection by the Costa Rican Institute of Water and Sewerage, known as AyA, found that wastewater discharged into Camaronal Creek did not meet current regulatory standards for several key indicators, including Biochemical Oxygen Demand, Chemical Oxygen Demand, and Total Suspended Solids.
The inspection also found administrative and operational gaps. The discharge point had not been registered with the Water Authority, required operational reports had not been submitted, and procedures related to environmental discharge fees had not been completed.
The plant uses a Bionest system, which depends on blowers to provide oxygen for the biological treatment process. AyA found three blowers out of service during the inspection. The report also pointed to problems with the station’s power supply, which has affected the system’s ability to function properly.
Maintenance has also been a major issue. Officials said the plant has received almost no maintenance over the past five years, despite needing regular servicing. Sludge that should have been removed every four to six years has never been extracted. Using Ministry of Health inspection guidelines, AyA determined that Sirena failed to meet more than 80 percent of the evaluated criteria. Missing items included operating manuals, maintenance records, approved plans, signage, and a paginated operational log.
SINAC’s Physical Infrastructure Department is scheduled to inspect Sirena from July 8 to 11 to determine the repairs needed. In the meantime, visitor capacity will be reduced through September. Through July, Sirena will be limited to 150 people per day, including 50 overnight guests and 100 day visitors. On July 27, the capacity will shift to 70 overnight guests and 80 day visitors.
During August and September, the station will receive a maximum of 100 visitors per day, divided between 30 overnight guests and 70 day visitors. Sirena will remain closed during October, as it normally does each year. Authorities expect most of the required construction and repair work to take place during that closure period.
Additional measures are also being applied. Beginning June 30, 2026, laundry operations must be moved outside Corcovado National Park until there is technical certainty that the treatment system can handle that wastewater. Restaurant occupancy at Sirena will also be limited to 90 people at one time, including visitors and workers, in line with Ministry of Health requirements.
MINAE said the measures are intended to protect Corcovado’s ecosystems while repairs are carried out. The ministry’s goal is to restore full operations at Sirena on December 1, 2026, with the wastewater treatment plant functioning properly.
