On a sun-battered stretch of the Miami River canal wedged between U.S. 27, the old cross-state truck route, and an industrial area of Medley, the water looks brown, murky and inhospitable.
For Ali Ebrahimian, a Florida International University engineer specializing in water resources, the location is perfect.
“Basically, these are our rivers,” Ebrahimian said one morning in February while two research students connected a pump in the bed of their pickup to suck up water from the canal. ”We’re trying to see what is being discharged into this water, and then what happens. All these pollutants have a journey.”
The location is just one data point in a pollution hotspot map Ebrahimian is building to better understand how stormwater is polluting groundwater across South Florida. That matters because as climate change warms the planet in bustling South Florida, more stormwater and all the stuff running off streets, parking lots, yards and more is mingling with the region’s shallow groundwater.
That’s troubling for the Everglades and Biscayne Bay because that water can contain nutrients like nitrogen and phosphorus that trigger algae blooms and fuel the growth of macro algae that smothers sea grass.
Yet across South Florida, Ebrahimian says, little is known about one of the primary ways stormwater is drained: French drains or infiltration trenches.
”Surprisingly, we don't really know their performance. We have never monitored their performance in detail,” he said. “We have just added them to our projects and they're working. So we are okay.”
Florida, along with the rest of the country, relies heavily on underground infiltration trenches or French drains —shallow perforated pipes that move stormwater while also allowing it to filter out. Miami-Dade County alone has more than 300 linear miles — about the distance between Miami and St. Augustine. In places where groundwater is deeper, dirty water can be filtered as it percolates through soil or rock to the water table below. But in South Florida, Ebrahimian said the groundwater is often the same depth as French drains, so the water has no chance to be filtered.
Backbone of the drainage system
The Miami River Canal is one of the backbones for South Florida’s drainage system. It starts miles away at Lake Okeechobee, then cuts a nearly arrow-straight path across three counties. After about 60 miles, it arrives here in Miami-Dade, where it dumps into Biscayne Bay.
“ It passes through different urban areas, including, for example, here in Medley, which is mostly an industrial area,” Ebrahimian said. “It goes through a lot of different urban land uses are around this, and all of them are discharging their stormwater runoff.”
So no surprise, the canal is chronically polluted. It has repeatedly failed to meet limits for fecal coliform, the bacteria found in human and animal waste. It contains nutrients, heavy metals and microplastics. Fish are loaded with mercury. The canal is also not unique. Canals across South Florida carry stormwater loaded with chemicals.
That’s where Ebrahimian's pollution hot spot map will come in handy, to identify where water in storm sewers and canals is most polluted.
Then, using the FIU campus as a lab, Ebrahimian and his students are investigating better solutions. For the past three years, they’ve been collecting and tracking pollution, including nutrients and micro plastics, near a campus infiltration trench.
”We wanted to see how these systems are working. Are these helping us here? And then how do we get water quality improvement or are we hurting our groundwater quality?” Ebrahimian said. ”We wanted to see if there's an effect, and if so, what is the radius of that effect?”
In the Everglades, Florida has spent about $2.5 billion to clean stormwater flowing off sugarcane fields that rely heavily on sprawling treatment marshes to scrub water. The marshes cover about 57,000 acres and cost between $35 million and $40 million annually to operate.
But in urban areas, where quarters are tight and the pollution seems to come from everywhere, solutions are more complicated.
“T he Clean Water Act is 54 years old now. And we spent a lot of time like, dealing with that problem, I'd say mostly successfully,” said Matthew Cohen, an ecohydrologist and director of the University of Florida's Water Institute.
Pollution that degrades water and habitats has been widely identified and limits set to protect bodies of water, he said. But in many cases, those ambitious limits never get met. South Florida canals and rivers, from Broward County to the Keys, are full of nutrient pollution. A 2025 study also found that water is consistently reaching reefs where it can damage coral. And this week, the Surfrider Foundation also reported that two beaches in Miami-Dade County ranked among the top 10 it monitors nationwide.
This year's Biscayne Bay report card also confirmed that nutrients and bacteria in canals and parts of Biscayne Bay remain at harmful levels. , The bay, groundwater and canals that feed the bay are facing "unprecedented threats" to their health and resilience, the report said.
“ That's a collective problem,” Cohen said. “That's us making decisions collectively that don't translate into, you know, we all want Biscayne Bay to look awesome. I don't think there's any constituency that thinks it should, you know, be an algal bloom.”
Nature's fix
So how to fix that? Wetlands are nature’s fix. They’re natural sinks where water gets trapped and cleaned as it slowly drains. But South Florida keeps paving over them.
Ebrahimian's solution: use the same strategy as the Everglades' sprawling treatment marshes but on a more nimble scale. And, he hopes, using existing ponds and other infrastructure.
On the FIU campus, the infiltration trench being monitored by his lab isn’t making nearby groundwater more polluted. But, he said, it’s also not improving water quality in a way that trenches or French drains used in areas with deeper groundwater do. So Ebrahimian is also studying a campus pond and wetland created to replace a similar wetland that was filled to create athletic fields, to mimic the strategy of the sprawling Everglades wetlands.
The tear-shaped pond is lined with sawgrass and filled with water lilies. Native trees spread into a nearby hammock. Spread across just 11 acres, the area is small enough to fit into urban neighborhoods.
“ This is a green infrastructure. The alternative approach was just to use storm sewers. Collect your water, then as soon as possible, connect it to your canals,” he said. “Same old, same old.”
But now, water flows from the nearby street into the wetland, where nutrients get consumed by plants or attached to sediment. A short walk away, a much smaller wetland, about the size of a yard, is filled with cypress trees. It's an oasis of shade next to the campus convocation center, holding and cleaning water.
“You can fit them where possible or where needed. You can just fit them in the existing spaces," Ebrahimian said. "These are the technical benefits, besides being beautiful."
This story was produced by WLRN, South Florida’s only public radio station at 91.3 FM, as part of a content-sharing partnership with The Biscayne Times. Read more at WLRN.org.