The Costa Rican Fisheries Institute (INCOPESCA) is working with national universities to determine what killed thousands of fish near the beach last week.
Researchers from the Center Of Microscopic Electronics at the University of Costa Rica (UCR) took water samples for analysis shortly after the kill occurred. They expect to have results before Friday.
Officials cannot confirm the cause of death until testing is complete, but said that a red tide – a harmful algae bloom that can suffocate marine life – or a chemical spill are both possible reasons for the large kill.
One researcher at the UCR told The Tico Times that red tides are normal this time of year, but said that both the size and the amount of the dead fish could indicate a different cause.
Red tides usually kill small fish, like sardines, and in smaller numbers, the researcher said.
Leonel Hernández, a Guanacaste resident, said he saw fish weighing as much as 14 kilograms, including sardines and other species, lying on the beach.
Marvin Mora, interim technical director of INCOPESCA, said citizens and tourists should not eat fish from Playa Lagarto until further notice. He said INCOPESCA will inform the public when the results of the sample analysis are complete.