PALMA SOLA BAY – The month-long pause in horseback riding in Palma Sola Bay and along its northern shoreline ended on Oct. 6 and the Sarasota Bay Estuary Program (SBEP) has released the results of its water quality testing.
Prior to and during the horses’ absence from the bay, SBEP sampled the water five times and received results from four of those tests by Oct. 8.
The role of the horses in the high bacterial numbers in the bay will require further evaluation, according to SBEP Executive Director Dr. David Tomasko.
“For all four times, the levels of enterococci – the state’s default “fecal indicator” bacteria – exceeded the bathing beach standard at the site where the horse ride operations occur,” Tomasko wrote in an Oct. 8 email to The Sun.
He said the results of the tests show there are sources of “fecal indicator” bacteria other than the horses.
“For the first two sampling events, the horse ride vendors were out there, and although we had detections of DNA sequences of bacteria that were from horses, the numbers were too low to be quantified. That is called a DNQ event “Detected, Not Quantifiable,” Tomasko wrote. “For the next two sampling events, the horse ride vendors were off the causeway, and we didn’t even have detections of the DNA sequences of bacteria from horses.”
Tomasko stated SBEP still has three more sampling events to work through, all with the horses now back on the causeway.
“When we have all the data together, the SBEP will have a better understanding of how to interpret the results from this study,” Tomasko wrote. “But what seems fairly clear – and which has been clear for a while now – is that there are sources of “fecal indicator” bacteria other than horses out there. We have hits for birds, but not humans.”
Tomasko said some of the “fecal bacteria” indicators may not be from fecal sources at all.
“We know that each of the three fecal indicator species used by the State of Florida can arise from decomposing vegetation, but we don’t know what role – if any – that potential source could have on what we’re finding in Palma Sola Bay,” he wrote.
Suncoast Waterkeeper has been monitoring water quality in the bay and posted the following on its website: “Our monitoring results reveal persistent exceedances of the state’s water quality standards for enterococci bacteria:
- 2022: 22 samples collected, 6 exceeded the FDEP threshold of 130/100 mL (no more than four should exceed);
- 2023: 46 samples collected, 23 exceeded (no more than eight should exceed);
- 2024: 43 samples collected, 20 exceeded (no more than eight should exceed); and
- 2025 to date: 32 samples collected, 16 exceeded (no more than six should exceed).”
Further testing showed the following results:
- April 2024: Horse DNA was detected and quantified in both water and sediment; no human DNA was detected;
- July 2024: Horse DNA was again quantified in water samples; human DNA was detected, but at levels below quantification; and
- April 2025: Avian DNA was detected at low levels; neither horse nor human DNA was detected in the sample.
“These findings demonstrate that horses are a measurable source of bacterial pollution in Palma Sola Bay north of the causeway; however, they are not the sole contributor,” Suncoast Waterkeeper Executive Director Abbey Tyrna wrote on the organization’s website. “The scientific literature emphasizes that microbial contamination in coastal waters frequently originates from multiple sources, including wildlife, domestic animals, and human infrastructure, and that distinguishing between these inputs and their relative contributions is inherently challenging.”
Tyrna does not support removing horses from the bay, but recommends the following:
- “Install Public Signage – Post clear warning signs alerting residents and visitors that enterococci levels exceed state water quality standards, so that people can make informed decisions about their health and recreation;
- Establish a Horse Vendor Permit System – Create a permit program that caps the total number of horse vendors and requires best management practices (BMPs) designed to protect water quality and seagrass meadows. Such BMPs should include ensuring horses remain in shallow water for the majority of the ride, only wading in past their hindquarters for a short duration at the beginning, and requiring the use of waterproof horse diapers. The permit should also stipulate the area where the horses can ride to protect the seagrasses.”
