Marco Island Water Quality Status Report August 2021

Marco Island waterways have been deficient for Dissolved Oxygen (DO) each month starting in October 2020. Since that time the entire waterbody has been deficient in DO each month, with the exception of December 2020 and January 2021. In 2017, 4% of all of the Marco DO readings were deficient. So far in 2021, 68% of all of the Marco DO readings are deficient. The trend is decisively negative and shows no sign of slowing down.

Dissolved Oxygen (DO) is viewed as a general indicator of waterbody health because it is essential to aquatic life. Since the 1970s and until recently, the marine water quality standard for DO in Florida required a minimum daily average of 5.0 mg/L. In 2013, FDEP adopted revised DO criteria for fresh and marine waters. The new marine DO criterion is based on percent saturation instead of concentration and requires DO to maintain a daily average greater than 42 percent saturation (Naples Bay Water Quality and Biological Analysis Report, October 9, 2020, Cardno).

A Hypoxia Investigation was finalized at the Marco Island Waterways Advisory Committee (WAC) meeting on September 16, 2021, and is available on the City of Marco Island website. This report directly links nutrients (nitrogen and phosphorus) in the reuse water from the Marco Wastewater Treatment Plant (WWTP) to oxygen depletion in the Marco waterways.

Let’s be clear, reuse water is treated sewage. “Reuse” is the politically correct term. Sounds like a good thing. What the state forgot when they promoted this program is the massive amounts of nutrients that come with this “water” that we use to fertilize the lush green grass in our public spaces.

Nutrients from the reuse water feed algal blooms that consume oxygen in the waterways leading to seagrass die-off. Hypoxia eventually leads to the death of all aquatic life in the waterways. We are now seeing Harmful Algal Blooms (HAB) on a regular basis in the Marco Island waterways.

When the DO level drops below 3.0 mg/L, the water is considered hypoxic. Hypoxia is oxygen depletion in waterways. Oxygen depletion is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system, such as fish, grasses, and oysters. Seagrass is a food source for Manatee.

Basin Five is the only completely healthy basin on the island; Basin Five gets NO reuse water from the Wastewater Treatment Plant (WWTP).

Eugene Wordehoff Citizen of Marco Island

Member, Waterways Advisory Committee to City Council