Silver Glen Springs is a 1st magnitude spring with a large, semicircular pool that is approximately 200 x 175 feet. The bottom around the main vent is mostly sand covered now, with algae that is perplexing scientists. This spring is also within the Ocala National Forest and discharges approximately 65 million gallons of fresh water per day.
The stripers and I were headed towards the vent at the same time from opposite directions. Soon they were everywhere. Silver Glen Springs is one of the most important and frequently used thermal refuges for striped bass in the St. Johns River system. I have never seen so many in one place. Though algae was primarily relegated to the sandy bottom, which was mostly devoid of natural grasses, there were also clumps of lyngbya wollei in the water column.
Lyngbya is a genus of cyanobacteria that contains a toxin that proposes a health hazard to humans and other creatures that come in contact with it. According to the British Columbia Ministry of the Environment, cyanophytes found in freshwater habitats experience cyanophyte blooms more than in any other habitat they are found. This report goes on to say the following about blooms:
"Two genera of cyanophytes account for the vast majority of toxic blooms world-wide: Microcystis and Anabaena. Anabaena and Nodularia have been implicated in skin and eye irritations in man and dogs, while Microcystis, Anacystis and Lyngbya have been reported to cause hay fever symptoms, particularly as aerosols. It has been suggested that toxic products released from cyanophytes may be the cause of unexplained forms of human gastro-enteritis. Microcystis aeruginosa, Anabaena circinalis and Nodularia spumigen blooms produce a characteristic pungent, musky or earthy smell. Fish deaths during cyanophyte blooms may be caused by the toxin in the cyanophyte, by the depletion of oxygen in the water, by the liberation of hydrogen sulphide and ammonia caused by cell decomposition or by clogging of the gills." (http://www.env.gov.bc.ca/wat/wq/reference/cyanophytes.html)
It was disturbing to see huge chunks of filamentous algae on the surface of the water. With much of the natural eelgrass beds destroyed, carp fish will sometime eat lyngbya wollei. The aforementioned report states that "all warm-blooded animals are susceptible to cyanophyte toxins, including people, waterfowl, furbearers, game and non-game animals, livestock, poultry and household pets." Though why algae makes people sick is known scientists really can't understand why there is algae here, as the springs are at least 30 miles from any agricultural development.
One theory for how there is so much algae in a spring located in a forest with extremely low nitrogen levels is that the algae mats produce enough nitrogen to sustain themselves. Another is that the increased salinity is favorable to their production.
It was magical swimming around with all these fish, watching them catch the light, and swim over the vent as the water poured out. The water they were heading towards was clean and algae free, but to get there they had to traverse areas that were murky and unsafe. This spring has also been designated as critical for manatee habitat, although I did not see any that day. In fact, their use of this area has been limited since so many natural grasses have been damaged by algae and human use. Many scientists recommend not swimming in areas where algae outbreaks have been reported. Sadly, in Florida that would not leave many springs left that are totally safe to swim in. The most at risk are children and pets, since they require less of the toxins to become ill.