The Potomac River once regularly ran green through Washington, D.C.—a bright, neon green caused by algal blooms.
In 1965, President Lyndon Johnson called the river a “national disgrace.”
It was widely regarded as a cesspool.
Pollution from farmland and urban centers like Washington and Baltimore filled the Potomac with nitrogen, and that nitrogen fueled the brilliant, green blooms of algae that choked the waterway and strangled its fisheries all the way down to the Chesapeake Bay. Few people dared to swim in the Potomac, let alone fish there.
The river was a far cry from the 1800s powerhouse that helped raise nearly half of America’s oysters in the bay.
That was before the 1972 Clean Water Act. That was a different Potomac River; one full of rampant pollution and home to a foul stench. In the past four decades, water quality in the Potomac has improved. Recreational use of the waterway has returned. And the rampant algae blooms have decreased—but they’ve not been completely eradicated.
In 2012, the Potomac was listed as the most endangered river in America. A year earlier, reports surfaced of toxic algal blooms causing sickness and leaving rashes on swimmers. Today, in 2014, the river and its fisheries are still very much in danger. NOAA says that high nitrogen levels have not dropped since the 1990s. But there is hope.
This month, scientists pinpointed an unlikely hero for the Potomac—the humble oyster.
According to a study released by NOAA and the U.S. Geological Survey, water quality pollution in the Potomac River could be reversed by oyster farming.
How? Oysters are filter-feeders. They thrive on the nitrogen released by urban runoff and agriculture.
The study says that if 40% of the Potomac River Estuary held populations of oysters, all of the nitrogen from pollution would be absorbed. In effect, the algae blooms would cease. “Dead zones” in the river, where pollution and runoff are most prevalent, could be held under-check.
But 40% of a 382 mile river system is a lot, even for oyster farms that could generate jobs in the seafood industry. It’s much more likely that only selected areas would be farmed; but even that, the study says, would have a tangible positive impact:
“The Chesapeake Bay and tributary estuaries such as the Potomac River, as with other water bodies worldwide, have experienced nutrient-related water-quality degradation for decades with consequent impacts to living resources such as sea grasses and cascading impacts on fisheries…Shellfish filter phytoplankton and detritus from the water, thereby reducing eutrophication [algae blooms] by short-circuiting organic degradation.”
The study falls in-step with the 2009 NOAA Aquaculture Policy and a 2009 Shellfish Aquaculture Plan from the state of Maryland. Oyster farming, it appears, is being recognized as a necessary compliment to anti-pollution legislation that already controls the output of industrial wastewater into the river. But unlike industrial wastewater output, which can be regulated through outfall points, oyster aquaculture can also address pollution runoff from broad swaths of agricultural runoff into the water.
The oyster farms would also be considerably more cost-effective than multi-million dollar plant-based filtering techniques. Together with existing plants and the restoration of oyster reefs, the oyster farms could restore critical levels of dissolved oxygen in the Potomac. It’s an effect that would help fish populations rebound.
And the green algae blooms on the Potomac? Scientists say the quickest way to see them gone for good is introduction of oyster farming alongside the existing treatment plants. “Results are promising with respect to nitrogen removal via aquaculture and reef restoration,” the study says.
It’s been 200 years since the Potomac River and Chesapeake Bay brought the majority of America’s oysters to market. Populations have declined due to overfishing and disease. But if NOAA and the USGS have their way, those populations could be on the rebound—and they could be doing it while bringing an entire river system back to life.