Officials say a bloom of Florida red tide remained over the weekend along beaches in and around Tampa Bay.
The Fish and Wildlife Conservation Commission says it has found concentrations in it high enough to kill fish and cause respiratory irritation in people.
Low levels of red tide have also popped up in Charlotte County and other places.
Red tide can cause people to cough and sneeze. It can also give them scratchy throats, and make fish and shellfish dangerous to eat.