Published: Nov 30, 2011 4:59 AM EST

SANIBEL, Fla. - Red tide is starting to turn up in higher concentrations off the Southwest Florida coast. But both scientists and tourist businesses say the growing algae bloom shouldn't be a cause for concern for most people.

"Right now the scale of the bloom is quite large," said Eric Millbrandt, director of the marine laboratory at the Sanibel-Captiva Conservation Foundation. The SCCF has been testing the water for red tide since the microscopic algae first appeared in the gulf.

"It's been persistent off shore and moving southward for the last month or so," Millbrandt said. "We've found the concentrations are high enough to cause fish kills."

Red tide can be toxic to sea life. Fish can no longer breathe underwater as the toxins make it difficult to move their gills.

The danger for fish isn't the same for people.

"It is absolutely safe to walk along the beach, if you don't have respiratory problems with it," said Bruce Neill of the Sanibel Sea School "Some people will experience coughing, some people will experience a unique odor."

In the past few days, high concentrations of red tide have been tracked off Sanibel and the Collier County coast.

"Around the causeway we were seeing half a million to a million cells per liter in several locations," Millbrandt said.

But there have been few dead fish found along the shores of Sanibel so far, and even fewer complaints from visitors.

"Red tide does not seem to be an issue with anybody who's coming in, they're all going to the beach, they're having a great time," said Barb Harrington, with Royal Shell Vacations and Real Estate.

Scientists say time and cooler water temps should help clear up the situation, although the exact timing is unclear.