A Red Tide bloom off the Gulf Coast is the largest associated with a fish kill since October 2006, officials said.The patchy bloom of Karenia brevis, the Florida Red Tide organism, is about 80 miles long, up to 50 miles wide and up to 50 feet deep, according to the Florida Fish and Wildlife Conservation Commission. It was detected 40 to 90 miles offshore between Dixie and Pasco counties, and researchers believe it is moving south."There's potential for a large fish kill because the size of the bloom is so large, and there's potential for large inshore human health implications because of the size of it, but . . . at the moment, it's still projected to move south and it's not ashore," said commission spokesman Brandon Basino. "Now, it's more of a matter of tracking it and predicting when and if it will come ashore."Red Tide refers to a higher-than-normal concentration of microscopic algae, named as such because the water often turns red or brown during the bloom. They release toxic chemicals in the water and air that are harmful to marine life as well as humans, especially those with respiratory problems.It has caused an ongoing fish kill in the northeast Gulf of Mexico. Basino said the Fish Kill Hotline has received reports of thousands of dead and near-dead benthic reef fish, including snapper and grouper species, grunts, and crabs, as well as water discoloration.Commission researchers left for a three-day cruise Sunday night and will return Wednesday morning. The cruise is being guided by satellite imagery and bloom forecasts with the help of more than 20 stations up to 70 miles offshore and covering about 2,000 square miles. Their goal is to measure concentrations of Karenia brevis in surface and deep waters offshore of Pinellas, Pasco and Hernando counties so they can construct a 3-D image of the Red Tide.Researchers will return with water samples that will be tested for nutrient concentrations and toxins. Basino said the tests will also help them figure out where the bloom is moving.Basino said swimming and fishing should be safe, but beachgoers should visit mote.org/beaches to check beach conditions.