Lemon, blacktip, bonnethead and nurse sharks have crowded into the waterway in Buttonwood Harbor.
The toxic algae had disappeared earlier this year after an abnormally long bloom.
The algal bloom has also killed fish, sea turtles and manatees along the Gulf Coast.
The bloom had been tormenting Florida's coastline inhabitants for well over a year.
Beaches were shut down in Palm Beach County and Miami-Dade County.
"Red Tide Rick has got to go," shouted demonstrators as waves of dead fish buried beaches.
The Florida governor enthusiastically slashed environmental programs during his two terms, but is now blaming the ensuing water crisis on his Democratic Senate opponent.
The algae bloom, which may have killed as many as 127 manatees this year, has reached the Tampa Bay area.
The harmful algae bloom has fouled the state's waters for months.
Dozens of manatees and hundreds of sea turtles have died in the longest-running red tide outbreak since 2006.