South Florida's beaches are having a bad year, being closed more often and for longer periods of time due to the presence of bacteria that is associated with sewage.
The chart above shows the number of advisories per year for beaches in Broward and Miami-Dade counties, according to data posted online by the Florida Department of Health.
The advisories are issued after tests confirm the water contains enterococci, a bacteria that indicates the presence of feces, at levels the state says can be unhealthy to swimmers.
When the number of advisories at each beach is plotted on a map, it is clear the hot spots are in the area of Key Biscayne.
And a closer look at the area that reports the most advisories reveals what some might consider a likely culprit (marked by the brown dot in the image above): the Miami-Dade County Central Wastewater Treatment plant on Virginia Key, which receives about 100 million gallons a day of what is flushed down toilets in the heart of the county.
That's a lot of feces.
But research by University of Miami engineering professor Helena Solo-Gabrielle finds no evidence the proximity of the plant is behind the more frequent reports of high levels of the enterococci bacteria on nearby beaches.
"We've looked at the relationships between what's going on at the wastewater treatment plants and the levels of bacteria at the beach and we do not see a correlation," she said in an interview with NBC6 Investigators. "From what we've observed, we don't believe it's the wastewater treatment plant."
Seconding that conclusion: Kevin Lynskey, the director of Miami-Dade Water and Sewer Department, which runs the plant.
"It certainly isn't the plant," he said. "The plants themselves are not responsible for this."
So what is?
"I don't know why they're not meeting state standards," Lynskey said of the beaches. "I really don't. It's a real mystery. There are many people looking into."
Including Solo-Gabrielle, who said she has found a connection between higher bacteria levels and conditions that push water farther and higher up the beach, such as high winds and king tides.
In and on the sand just above the normal water line are several potential boosters of bacteria, including waste from dogs and birds and seaweed, she said.
"We find they tend to accumulate in the sand right above the high tide line," she said, adding when winds pick up and push water into those zones, bacteria wash back into the water near the beach, where it can thrive.
While her findings so far do not show the wastewater plant causing the problem, others who test the waters say that may not fully exonerate the plant as a contributor.
The UM research uses, in part, reported spills and leaks from the plant.
Lynskey said – and county reports to the Environmental Protection Agency show – there are very few events like that at the plant.
But Collin Schladweiler, outreach coordinator for the environmental group Miami Waterkeeper, said not all laks may be known or reported.
"There might be a lot more sewage leaks that we don't know about," he said. "The one in 2016, for example, leaked for over a year and we didn't know about it."
He's referring to a break in the three-mile-long outfall pipe that runs form the central plant out into the ocean. Miami Waterkeeper showed it leaking through the ocean floor about a mile off the coast in 2016 and sought to force Miami-Dade to repair the leak, which it eventually did.
Lynskey said that water was treated with chlorine to a degree where it was actually cleaner than the ocean water it was leaking into.
Whatever is causing the more frequent beach advisories, the Department of Health warns swimmers in bacteria-laden waters can get gastrointestinal sickness, rashes or, if they come in contact with open wounds, more serious problems.
Dr. Solo-Gabrielle said the benefits of a day at the beach outweigh the risks posed by the water at normal levels.