Marco Island Waterways Impaired for Low Oxygen

During the month of August 2023, the Marco Island waterways were technically impaired for low oxygen with an average oxygen saturation level of 41%. The official oxygen impairment limit for Marco, as established by FDEP, is 42% Dissolved Oxygen Saturation % (DOSAT%). This is a low point in the health of the Marco waterways and is the first time in recorded history that the waterways tested below the oxygen impairment threshold.

Oxygen is an essential component of the aquatic environment. The most important and commonly used measurement of water quality, it indicates a waterbody’s state of health - that is, the ability to support aquatic life. 

Excess nutrients (phosphorus and nitrogen) delivered to a waterbody can lead to both overgrowth of algae and eutrophication. As dead algae decompose, oxygen is consumed in the process, resulting in low levels of oxygen in the water. Because there are increasingly more people living in coastal areas, there are more nutrients entering Florida’s coastal waters from wastewater treatment facilities, runoff from land in urban areas during rains, and from farming.

It is interesting to note that all impaired sampling locations on Marco are in areas where wastewater sewage reuse water is heavily used for landscape irrigation: Condos along the beach and two golf courses. 

This does not mean that the Marco waterbody is “officially” impaired. FDEP will only put a waterbody on the “impaired list” when it has been fully impaired for 2 consecutive years. If the current trends hold, Marco might be officially declared impaired for oxygen in 2027. What will be the impact to property values and our tourism-based economy?