NAPLES (AP) — Officials say they’ve found traces of red tide on some Collier County beaches.

The Naples Daily News reports red tide monitors found levels of red tide at various concentrations along the beaches this week. Some dead fish were reported on Barefoot Beach on Wednesday.

Red tide is microscopic algae that can release toxins poisonous to marine life. It can cause respiratory irritation.

Collier County’s pollution control officials say patches of water with elevated to very high levels of chlorophyll were visible on satellite imagery on Wednesday. They say this is another indication of possible red tide.

Officials are cautioning people with asthma and emphysema to avoid the beach until the toxin levels are reduced.