Experts warn Sarasota Bay water quality suffers after Debby

Experts with Suncoast Waterkeeper and the Sarasota Bay Estuary Program agree: It’s not safe to swim in the bay right now. 

A week after Hurricane Debby dumped large amounts of rain on the Sarasota Bay area, local experts are cautioning the public about potential negative side effects to the safety of the bay. This includes the reported millions of gallons of sewage discharged from municipalities that entered local waterways.

These impacts, and more, came from then-Tropical Storm Debby’s copious rainfall, which overwhelmed wastewater systems and brought pollutants into the bay. The full scope of the impacts is still to be determined. 

“You can’t have this much rainfall without water quality being adversely impacted,” said Dave Tomasko, executive director for the Sarasota Bay Estuary Program. 

Trickle-down effects 

Shortly after Debby passed, municipalities reported wastewater failures and estimates of how much sewage flowed into surrounding water systems began.

The latest reports from the Florida Department of Environmental Protection estimate that 25 million gallons of sewage from the city of Bradenton’s system flowed into Manatee River, according to Suncoast Waterkeeper Executive Director Abbey Tyrna. Another 17.7 million gallons are estimated to have leaked from the city of Sarasota into Sarasota Bay. 

“I don’t think it’s an exaggeration to say that the nearly 1 million people in Sarasota and Manatee counties basically used Manatee River and Sarasota Bay as a toilet on Monday,” Tyrna said, referring to Monday, Aug. 5, the day of Hurricane Debby’s main impact on the region. 

As a result, Suncoast Waterkeeper issued no-swim advisories for Sarasota Bay until further notice. 

Tomasko and Tyrna both said the problem largely has to do with aging collection systems, which caused failures in the region’s stormwater and wastewater systems. 

“Everyone pays a lot of attention to the waste treatment plant, but the real problem is getting to the plant,” Tomasko said. 

The two explained that when significant rainwater and flooding occur, the ground becomes heavily saturated. If wastewater systems have older pipes — aging infrastructure — then that excess water in the ground can seep into the pipes and cause more water to flow into the treatment plants than what the plants can handle. 

That’s how the plants commonly become overwhelmed, leading to incidents like the ones that occurred with the city of Bradenton and the city of Sarasota. 

“So when you see standing water on the streets … that means that the groundwater is completely saturated, which means the water that’s in the soil can make its way into the stormwater collection pipe and overwhelm the capacity of the plants,” Tomasko said.

Photo by Carter Weinhofer

Inundation of lift stations that move wastewater from low elevations to higher ground also played a part in the recent pollution problems, Tyrna explained. 

Another component of Debby’s pollution is from land-based pollution sources, things like over-fertilized lawns, grass clippings and animal waste. 

Tomasko said he’s also seen the impact of grease from flooded cars and boats, septic tanks from boats and spare gas cans trickling into the bay from flooded vessels. All these things, from sewage that leaked into the water to car grease, could play a part in potential negative side effects to come. 

Current conditions 

When Debby passed, bay experts began seeing the impacts and wondering about the coming weeks. 

“What we anticipate is that we’re going to have problems with algal blooms, potentially fish kills, high levels of bacteria,” Tomasko said. “It’s not an unrealistic expectation.”

Harmful algal blooms commonly occur from “overfeeding,” which happens when increased levels of nutrients are introduced into waterways from runoff, like nitrogen from fertilizer runoff or other bacteria, according to the National Oceanic and Atmospheric Administration. 

Tyrna’s organization, Suncoast Waterkeeper, conducts regular monitoring of water quality and releases weekly reports from about 11 sites around Sarasota Bay and Palma Sola Bay. After Debby, readings for enterococci — an indicator of fecal matter — were high in some sites. 

A “safe to swim” range of enterococci is between 0-35 bacteria per 100 milliliters (mL) of tidal water. On Aug. 7, some readings were 41 bacteria per 100 mL at the Longboat Key boat ramp and 2,143 bacteria per 100 mL at Bayfront Park in Sarasota. 

Tyrna also said that during this week’s readings, the salinity in the areas was surprisingly low. 

An average salinity level is around 25 parts per thousand (ppt), Tyrna said, and she was seeing some levels below 5 ppt. 

This could be due to a lot of rainwater flowing into the bay, which can negatively affect marine organisms that rely on saltwater. Some species cannot survive in salinities that low, and Tyrna said she wasn’t sure how long those impacts would last. 

High levels of enterococci bacteria and low salinity suggest that significant sewage and rainwater seeped into the area’s bays. 

Courtesy of the Sarasota Bay Estuary Program

Tomasko said the pattern of worsened water quality is common after storms that bring as much rainfall and flooding as Debby. 

“I’ve gone out monitoring after a storm event for 20 years now, and it’s a pretty consistent finding: you’ll get algal blooms, you’ll get fish kills and you’ll have high bacteria in the weeks after that,” Tomasko said. 

After Hurricane Ian, Tomasko said a similar situation unfolded. For at least two weeks after Ian, he said Sarasota Bay had poor water quality but, after about a month, the bay mostly recovered. 

“One good thing is, this bay is healthier than it’s been in the last 10-15 years, so we should be able to bounce back from it,” Tomasko said. “It’s an episodic impact, it’s not a chronic impact.”

Tyrna was more cautious, though. She said that while the bay may mostly recover, the sediments under the bay can act as reservoirs for the harmful bacteria. Then, when future storms cause a disturbance, those toxins could be stirred back into the water column. 

“It’s not like you just dump sewage into the bay and then two weeks later it’s gone,” Tyrna said. “A lot of it’s gone. But there’s still the reservoir at the bay bottom.” 

For now, Tomasko said people may start to notice water having a darker color, maybe brown. The color should be closer to aquamarine, he said, when it’s healthy. Basic senses should be an indication of whether the bay is safe, according to Tomasko.

“When the water looks the way it does, when it smells the way it’s going to smell in a while … just let your senses tell you whether or not it makes sense to go into the water,” Tomasko said.

Future upgrades 

“There’s a roadmap to upgrading your infrastructure to ensure that it’s resilient against these storm events,” Tyrna said. 

Replacing aging pipes, for example, is one way to prevent the excess water from overwhelming the collection systems. These projects take time and money, but will be necessary moving forward Tyrna said. 

These upgrades are especially important considering that some experts are warning about the impact climate change has on worsening storms. 

Tomasko said that as temperatures rise and the air is as warm as it is, the air can hold more moisture. More moisture leads to more rainfall. 

“All that flooding, all the damage (Hurricane Debby) did, that’s a tropical storm 100 miles offshore,” Tomasko said. “What are we going to do if we actually have a major hurricane, not a tropical storm 100 miles away. … This should be a wake-up call of: How prepared are we for a future with more storms?”

Tyrna said the same, and emphasized that tropical storms will continue to bring huge amounts of rain because of warmer temperatures. 

“And that’s why it’s important that we prepare,” Tyrna said.