Solving Marco Island Water Quality Problem

Oxygen in the Marco canals has dropped 70% over the last four years. Oxygen is the most important water quality indicator - essential to all aquatic life. No oxygen – no life.  

Phosphorus is one of the watershed pollutants monitored by the Florida Department of Environmental Protection (FDEP). As of October 2024, phosphorus levels in the Marco canals exceeded the FDEP limit. The Marco canals may complete the first year of phosphorus impairment in 2025. The indicator of algal biomass (CHLA) is also approaching the impairment limit. Marco is now officially impaired for low oxygen trend. The Marco canals are approaching “triple impairment” status. Not good. 

What causes the low oxygen in Marco canals? Two data sources were compared. The city measures phosphorus in sewage reuse water distributed as irrigation water. The city also measures oxygen in fourteen canal locations. Comparison of these two data sets showed a strong statistical correlation between high phosphorus in the sewage reuse water and low oxygen in the canals. 

What does science say about the connection? Nutrients in the sewage reuse water, nitrogen and phosphorus (think fertilizer), feed algae in the canals. Low levels of algae are always present. When the equivalent of 70,000 bags of fertilizer from the reuse water are added to the canals each year, the algae population explodes. This is one bag of fertilizer for each canal every day. Decomposition of dead algae consumes canal oxygen.  

Oxygen is dropping and phosphorus is increasing, indicating the existence of a major environmental problem in the Marco canals called “eutrophication.” No oxygen for the fish. No food for birds and other wildlife. Algae in the water column blocks sunlight and the seagrass dies–this means no food for manatee. The algae scum on the surface of the canals stinks and is toxic. No swimming in the canals. 

There is only one source of phosphorus on Marco Island – the sewage reuse water! The Marco eutrophication problem is an unintended consequence of the sewage reuse program implemented to save the Florida aquifer. 

The solution? Cleaning the nitrogen and phosphorus out of the sewage reuse water will eliminate this pollution at the Source. In late 2022, the city of Marco Island issued a Request for Information (RFI) for technologies to clean nutrients out of reuse water. One of the responses was from a firm used by FDEP to prevent a major environmental catastrophe at Piney Point (the equipment was installed in 17 days by a firm called NuQuatics). The cost to “polish” 97% of the nutrients out of the Marco sewage reuse water was estimated to be between $3-5M. A lease option might be available. A grant from the FDEP Innovative Technologies Portal might cover 100% of the cost. A “shovel ready” project. 

There is substantial public support for this solution. Several boards have issued letters to the Marco City Council supporting this project: Marco Island Civic Association (MICA), Marco Sportfishing Club, Marco Island Sail & Power Squadron (MISPS), Clean Marco Waters, LLC, and Marco Island Historical Society (MIHS).