Imagine that you are boating along the coast of Florida, enjoying the sun and looking forward to a little fishing when you realize something is wrong. You stop the boat, look around, and see that instead of being blue, the ocean is black. If you were on the southwest coast of Florida earlier this year, you could have had this experience.

This phenomenon has been called ...

The Black Water started showing up sometime in mid-January. By the time it peaked in February, it covered a 700 square mile area. The water was described with terms such as ‘snotty’, ‘nasty’, and ‘viscous’. If the appearance of the water wasn’t enough to warrant concern, the fact that fishermen were not finding any fish in the Black Water was alarming. Floridians are familiar with many different water quality issues, but this was something no one had ever seen before.

While research has answered some questions, there is still a lot that is unknown about the mysterious Black Water. A diatom bloom was the cause of the dark coloration of the water, based on data and samples collected during March. Diatoms are a different type of algae than those that cause the Red Tide. In fact, research showed very few if any of the Red Tide causing algal species in the Black Water. This was important because one theory about the origin of the Black Water was that it may have been related to a Red Tide event that had been occurring off of the Florida coast since August 2001.

Along with few Red Tide algal species, fishermen and scientist were not finding many fish in the Black Water. Reports were that there wasn’t a large fish kill, but instead fish seemed to avoid the water. Organisms that were not able to swim away from the bloom were not so lucky. Bottom dwelling sea sponges and soft coral where found either dead or dying in the Black Water. There were also reports that sea turtles that had eaten sea sponges were becoming ill with an unexplained pneumonia.

Even though the Black Water started to appear in January, real investigation into what it was and where it came from did not get underway until March. By this time, the bloom was in decline and the intensity of the Black Water was only 10% of what it had been in February.

The delayed reaction to the phenomenon may have cost scientist a few answers, and left them to only be able to theorize about the causes of the Black Water.

Along with the Red Tide theory, others felt that nutrient inputs associated with December rains may have provided just the right conditions for the bloom. Those pointing to runoff as the catalyst can make a strong argument. Southern Florida experienced two and one half times the normal rainfall in December 2001. This could cause high loading of nutrients into the bay. Algal blooms are often associated with changes in the environment that create perfect conditions for algal growth.

The weather anomaly of December may have been significant enough to tip an environment that has been facing increased impacts over time. In the 1980’s agricultural runoff was diverted from Lake Okeechobee into the Florida Bay. In 1981 there were 750 tons of nitrogen flowing into the bay, this increased to 2,500 tons in 1982. The load of nitrogen continued to increase and peaked in 1995, when almost 5,000 tons of nitrogen made its way into the bay. Over time, these impacts may have taken a toll on the bay’s resiliency, leaving it out of balance and susceptible to an extreme event such as an algal bloom.


Red Tide – Toxin producing algae that can, when in high concentrations, lead to fish kills, contaminate shellfish and create severe respiratory irritation in humans.

Sea Grass – Pollution may be killing off sea grass in the western Florida Bay. This leads to a loss of habitat as well as a loss of a natural filtration system that takes nutrients out of the system.

Coral Bleaching – The whitening of coral in response to a stress. The stress may be disease, increased shading, increased ultra-violet light, changes in salinity, changes in temperature, sedimentation or pollution.

Cellulitis – An infection that commercial fishermen have recently been dealing with. The infection spreads easily and can only be treated with stout antibiotics. Described as a “flesh-destroying” infection.

Will we see another episode of Black Water in the Florida Bay? Only time will tell. Time will also tell us what the long-term impacts of the bloom were. There are many water quality concerns associated with Florida, and this past winter another one was added to the list.

Dan Obrecht

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