Costa Rica said Monday there was no health impact from a shipwreck that spilled ammonium nitrate off its coast, but maintained a fishing ban even as it reopened beaches.

Authorities declared a red alert for the beaches around Puntarenas, a Pacific port popular with cruise liners, after the ship sank in rough seas Saturday while carrying 180 tons of the chemical, which is used in fertilizer and explosives, and can cause vomiting and seizures.

But Deputy Health Minister Maria Esther Anchia said the alert was preventive and that officials had now determined the waters were safe for swimming.

"There has been no impact on people's health," she told local radio station Monumental.

"The product dilutes very quickly."

No hospitals have reported patients admitted for ammonium nitrate poisoning, she said.

But the National Emergency Commission (CNE) maintained a ban on fishing in the area while it assesses the impact on marine life, a process it said takes about 72 hours.

Puntarenas sits 90 kilometers (55 miles) west of the capital San Jose and is a popular spot for beach getaways.

It is a gateway to the Pacific region for many cruise ships.

Costa Rica has a thriving tourism industry built around its pristine beaches and the stunning biodiversity of its tropical forests.