Biscayne Bay is polluted. Miami-Dade hopes this new technology will help clean it up

Pollution and water quality have long been an issue in Biscayne Bay, where stinky fish kills have become a summer norm, and every heavy rain washes a cocktail of oil, fertilizer, and wastewater into Biscayne Bay and its canals.

Miami-Dade County has invested millions to fix the problem and to modernize drainage systems, which threatens the tourism economy that relies on the health of the bay. Stormwater “is one of the major sources of pollution, from the land into our waterways” says Miami Waterkeeper’s CEO Rachel Silverstein.

The latest attempt to reduce the pollution input from stormwater is a series of pilot projects to filter water flowing from cities into the bay. Scientists are hopeful this rainy season will be the proof they need that these projects were worth the investment.

And, they say, they need residents’ help too.

Pilot projects underway

The latest solutions from Miami-Dade County to fix the polluted bay include three new projects to improve infrastructure — all different variations on advanced filters to clean dirty street water.

In the last four years, the county has won more than $22 million in grants from the state of Florida focused on stormwater pollution and flooding. The grants cover water testing, new technology, education, and outreach. A goal of these projects is to eventually implement green technologies, such as bioswales — vegetated areas that naturally filter runoff before it reaches the bay. Public spaces are also used to reduce flooding by catching and storing water rather than sending it down into the stormwater system.

These new projects incorporate traditional grates for removal of solid waste like plastic bottles but also use a multilayer filtration system that mimics the way forests and wetlands naturally purify water. As rainwater rushes in, it passes through a series of chambers lined with porous rock, sand and biofilters. These materials trap sediment, absorb heavy metals, and remove fertilizers, waste, and pollutants before the water is released into the canals and, eventually, Biscayne Bay.

All three projects use slightly different styles of filtration to catch slightly different types of pollution, like one designed to catch runoff from roads and cars and another designed to clean up extra fertilizer as it washes off yards and parks.

Liza Herrera, the lead engineer at the Department of Public Works at Miami-Dade County, and her team chose these technologies to tackle problems of bacteria and nutrients like phosphorus and nitrogen leading into the bay.

Engineers and environmental advocates hope that these costly investments will improve bacteria and nutrient levels in Biscayne Bay. The Department of Environmental Resources Management (DERM) will conduct tests this rainy season to determine whether the projects are improving as much as expected.

A long-term problem

Biscayne Bay is essential for recreation, fishing, and boating for residents of Miami and is home to wildlife in the area. The once clear canals flowing into the Bay are now unusable by several residents’ standards.

Dirty stormwater has been a decades-long problem worsened by urbanization and extreme weather events. In Miami’s concrete jungle, water rushes over paved streets, picking up contaminants rather than being absorbed by soil and vegetation.

Miami’s drains are outdated, experts say, built for an era of Miami with less development and less frequent flooding. As storms grow stronger with climate change, the system is overwhelmed, spilling untreated runoff into sensitive waterways.

To understand the increasing flow of dirty stormwater into the system, Miami Waterkeeper and Miami-Dade County put together an audit of the stormwater systems among different municipalities in 2022.

All municipalities averaged a C- rating in compliance from 2020. Among other things, Silverstein speculates that this is due to a resource disparity, with certain municipalities such as Miami Springs, Opa-Locka, Virginia Gardens, and El Portal having limitations in staffing and resources and the lowest scores of compliance (49%, 47%, 39%, and 37%, respectively).

“We’re giving them a few years to incorporate the outreach that we have been doing,” she said. Miami Waterkeeper is working with those municipalities to improve their compliance scores using recommendations to better understand their role in stormwater’s contribution to the overall pollution in Miami.

By the end of the year, results from DERM’s test of the pilot projects should show improvements, but Herrera said the second most important step is involvement from the community. “We need someone with a voice, and we need many voices to carry the message. Engineers know it. Chemists know it. I know it. It is a very select group of people that are aware of these issues. It does not get to the public.”

She and her colleagues say residents can reduce littering and minimize parking on grassy areas near stormwater drains, which are designed to collect water when it storms and floods.

The story was produced in partnership with Florida International University’s Caplin News.