Southwest Florida is warily watching the approach of another red tide invasion to its shores one year after a toxic algae bloom cost the tourist and fishing industry millions of dollars in losses.
While algae blooms are essentially tiny plants in the ocean that provide food for animals, harmful algal blooms, or HABs, multiply out of control, producing toxic or harmful effects for people, fish, shellfish, marine mammals and birds.
Red tide, caused by the organism Karenia brevis, occurs naturally in the Gulf of Mexico but is thought by many water quality scientists to be fed near shore by excess nutrients coming from the historic Everglades, which stretches from just south of Orlando to the Florida Keys.
Farm runoff containing nitrogen and phosphorus also feeds the bad algae and triggers explosive growth.
The Florida Fish and Wildlife Conservation Commission reports a new outgrowth of a troubling bloom along parts of the southwest Florida coast last week, particularly around Sarasota, Charlotte, Lee and Collier counties.
While this year's bloom, so far, is not as extensive or deadly as last year's, the outbreak is strong enough to kill various wildlife species that depend on coastal food and habitat.
"We have definitely been seeing red tide patients for several weeks now," said Joanna Fitzgerald, director of the Conservancy of Southwest Florida's von Arx Wildlife Hospital in Naples. "The main ones are the double-crested cormorants (seabirds). They're the big (indicator species). When you see them stumbling along the beach, you know what's going on."
What is red tide? A look at how red tide sparked a state of emergency in Florida last year
In a 1996 bloom, 149 manatees died off the coast of Florida while more than 740 bottlenose dolphins died from 1987 to 1988 after eating contaminated fish, according to Smithsonian Ocean.
The bad blooms can also be an irritant for swimmers, causing eye, skin and respiratory ailments, and are particularly dangerous to consumers of tainted shellfish.
Red tide may be most severe for people with preexisting respiratory conditions, such as asthma, according to the National Oceanic and Atmospheric Administration.
Last year, Florida businesses reported nearly $150 million in losses from the killing of fish and other marine creatures that had littered beaches and drove off tourists.
The scope of a threat from red tide is how tightly the microscopic cells are concentrated in the ocean waters. The cells are normally found in concentrations of 1,000 cells per liter of water or less, which is harmless. But once it hits 10,000 cells per liter of water, fish begin to die and humans and other animals can experience breathing irritation, the Florida Fish and Wildlife Commission says.
In last year's red tide calamity, counts of 1 million cells per liter and higher were reported from the Tampa Bay area south to Everglades National Park.
That bloom spread as far as the east coast and Panhandle, killing millions of fish and eels, hundreds of dolphins and sea turtles, untold numbers of birds and even a 27-foot whale shark.
In Lee County - the epicenter of the bloom - the recreational fishing industry and the local tourism- and real estate-driven economy were hard hit, leaving beachfront restaurants and hotels largely empty.
The lifespan of blooms is highly unpredictable. After one moves into an area, it steadily grows and within a few weeks, can reach concentrations deadly for fish. In the development stage, winds and currents shift the bloom around and - if it moves inshore - nutrient runoff may spur its further growth.
The Florida wildlife commission says a bloom can linger in coastal areas for days, weeks or even months.
Such blooms are "a national concern because they affect not only the health of people and marine ecosystems, but also the 'health' of local and regional economies," according to NOAA.
In Washington, the House passed a bill in September aimed at finding a solution to the red tide plague. A Senate committee was scheduled to take up a similar bill this week.
Contributing: Chad Gillis, Fort Myers News-Press
This article originally appeared on USA TODAY: Red tide Florida: Toxic algae bloom returns to southwest beaches