Thousands of dead fish, mostly sardines but also sea bass, are covering several small beaches in the Nicoya Gulf since Tuesday night.

Executive president of the Costa Rica Fishing and Aquaculture Institute (Incopesca), Gustavo Meneses, confirmed to national media that the affected area is of around 2 kilometers (1.25 miles) along several small beaches and the Moraga estuary in Puntarenas

The most affected area is Ensenada, but also Piedra Santa and La Mona, neighbors of the area made the report to Incopesca alerted by the large number of fish and the strong smell.

Incopesca is currently working along with the National Animal Health Service (SENASA) and coastguard to collect several samples and carry out different tests with the hopes of finding an explanation to the unusual phenomenon. They expect to have a result by next week.

“This is very atypical, not only because of the large number of fish found, but also because of the species, both these fish are around the same size, and the fact that they are appearing in this one specific place, we have a very healthy Nicoya Gulf, this makes it unusual”, said Meneses.

Ginés Valerín, Biologist from Incopesca, said one of the possible causes could be low levels of oxygen due to a type of seaweed, but this is only a hypothesis and they will need to wait for the results of the lab tests to confirm, she discarded the possibility of poison since only two species were affected.