Preliminary tests show red tide may be the cause of breathing problems some beach goers on Florida’s Atlantic coast have experienced.

Palm Beach County officials said yesterday state water tests found the algae that causes red tide. The statement said more testing needs to be done to determine its concentration before a final determination can be made. At least six beaches in Palm Beach County have been closed to swimming as a precaution, though officials are planning to reopen them Wednesday.

Florida’s Gulf Coast has been hit hard by red tide this summer, causing a massive die off of both fish and other sea life. It also causes breathing problems in some humans. There have been 57 Gulf Coast outbreaks since 1953.

Officials say red tide is uncommon on the state’s Atlantic Coast, with only eight outbreaks since 1953.