Wastewater in the Florida Keys Contributing to Coral Reef Decline

What stinks?

Sewage being ejected into a marine environment. Photo source: ourfloridareefs.org

Sewage being ejected into a marine environment. Photo source: ourfloridareefs.org

The troubled sewage history of Key West and the rest of the Florida Keys is extensive, extending back long before the times of Ernest Hemingway and his infamous 6-toed cats. Traditional methods of waste disposal involve ejection directly into the environment, which can occur over terrestrial landscapes, into ditches, shallow wells, lagoons, and streams. Since civilization in the Florida Keys is stationed atop porous limestone, this can pose further leaching into the environment and cause potential threat to Florida’s underground fresh water aquifer. Additionally, this poses risk to North America’s only living barrier reef located along the Florida Keys. Runoff and leaching of wastewater inputs large quantities of untreated or partially treated organic and inorganic nutrients and toxins from sewage, fertilizers, and other pollutants that can lead to increased occurrences of deadly red algae blooms and macroalgae that carpets coral reef communities and deprives them of life [b].

Before 1979, raw and untreated sewage was dumped directly into the Atlantic Ocean. Central facilities were hard to reach remote areas that had reverted to 8,000 unregulated cesspits discharging a combined estimated 1,200 pounds of nitrogen and 326 pounds of phosphorous a day into the surrounding marine environment. Septic tanks are also common where central water treatment facilities could not bear the expense of drilling through the limestone foundation and expanding pipelines throughout the 120 miles of chain islands [d]. Both methods for waste disposal carry risks to the environment and human health.

Clean and fresh nutrient-free water is essential for healthy coral reefs, which have from 30-40% live coral cover. However, the coral communities in the Florida keys only have about 3%. These are alarming statistics and the Florida Keys are not alone in their dwindling live coral numbers. Global populations of corals are facing the same decreased coral spawning instances due to threats against their environment [e].

Treated or partially treated sewage or ground water runoff laden with fertilizers into waterways is inputting an influx of nutrients, like nitrates and phosphates into coastal ecosystems. The over-abundance of nutrients in the ocean is thought to be the single biggest threat to Florida’s coral reefs. Their presence in the waterways causes eutrophication from rapid red algal blooms (a.k.a. red tides) that compete with corals for space. Additionally, deficits of oxygen can contribute to the death of surrounding fish and other marine life that help keep other species of algae in check [b]. A loss of herbivores can lead to further declines in coral reefs towards a macroalgal-dominated community [a].

Coral colony dominated by macro algae. Photo source: www.fmap.ca

Coral colony dominated by macro algae. Photo source: www.fmap.ca

Is Algae So Bad?

The presence of macroalgae in marine systems is an important component to the marine environment. Many species of fish, invertebrates, and other organisms rely on them intensively for food and protection. Sea turtles spend their days leisurely chomping on algae along with other aquatic plants, and certain fish and invertebrates hide in them from predators; parrotfish intensively work on cleaning corals of algae, scrapping them with their teeth and pooping out sediments onto the ocean floor, which can provide valuable substrate. Humans in many cultures eat various kinds of algae, or rely on the reef fish the inhabit coral ecosystems as sustenance.

Zooxanthellae (a.k.a. golden algae) is another essential algae that lives inside coral tissues. The algae provides uv-like protection, nutrients, and helps the coral to remove wastes. They are also responsible for the vibrant colors you may be most familiar with when thinking of coral reefs. In return, the coral provides protection. In order for this mutualistic relationship to succeed, the algae requires clear, low nutrient waters with little turbidity in order to absorb sunlight for photosynthesis.

Florida Keys Cleaning Up Its Act

Florida Keys has been slowly cleaning up its act. In 1999, the state ordered that Monroe County begin its transition towards a complete central sewage system. Sixteen years and nearly $1 billion later, the sewage system is close to completion, with 10 of the 12 major areas connected. One of the last two areas has been met with resistance. Located in one of the most geographically complex areas, the Cudjoe Regional Project spans over 10 bridge crossing from mile marker 33 in Pine Key to mile marker 17 on Sugarloaf Key. Some of the homes here are so remote, that they will be hooked up by alternative means involving on site systems [c].

Controversy revolves around the type of systems being implemented, with disagreements between the use of more reliable gravity pumps vs. low-pressure grinder pumps that are susceptible to power outages. Given the hurricane history of Florida, residents are up in arms about the risks of back flooding into their homes and contamination of groundwater. Others are upset about the idea of treated water that will be injected into 4 shallow wells [c].

In some of the other 10 areas where the central sewage system are up and running, residents have seen great improvements in water quality along the coasts. A Key Largo Resident and world-renowned underwater photography, Stephen Frink has said that, “while I saw an almost immediate improvement in the canals, this year I also saw new coral growth. And I was seeing a lot of really good fish.” [c]

We can only hope for the same sort of improvements. Keeping our fingers crossed that all of Florida Keys will get their s**t together. New signs of coral growth is a really great thing.


a. Collado-Vides, Ligia, Leanne M. Rutten, James W. Fourquerean. “Spatiotemporal Variation of the Abundance of Calcareous Green Macroalgae in the Florida Keys: A Study of Synchrony Within a Macroalgal Functional-form Group.” J. Phycol. Phycological Society of America, 41: 742–752. 2005.

b. Diersing, Nancy. “Water Quality: Frequently Asked Questions.” Florida Keys National Marine Sanctuary. 2009.

c. Clark, Clammy. “The big billion-dollar stink over sewers in the Keys.” Miami Herald. 16 August 2014.

d. Darden, Heather. “Wastewater in the Florida Keys: A Call for Stricter Regulation on Nonpoint Sources Pollution.” J. LAND USE & ENVTL. L. 16:2, 199-224. 2001.

e. “Florida Keys Reefs.” Reef Relief Founders.

f. “Water — Linking the Entire Southeast Florida Ecosystem.” Our Florida Reefs.