One of the largest dead zones in the Chesapeake Bay in decades has formed.
They call it bad water, and it spreads across the bottom of the Chesapeake Bay every summer. Watermen know that if they leave crab pots at depths of more than 10 or 12 feet this time of year, anything they catch will suffocate in a layer of water starved of oxygen.
And this season, the volume of that water — known ominously as the dead zone — is among the largest in the past 35 years.
That is evident not just in water samples scientists have collected to evaluate the dead zone, but also in crab pots and fishing nets from the Bay Bridge to Virginia. More often and more unpredictably than normal, some watermen are finding their catch dead by the time they pull it out of the water.
“The dead zones are getting bigger, and they’re getting more deadly,” said Don Pierce, a waterman from Rock Hall.
It is perhaps one of many signs the Chesapeake is suffering a hangover from more than a year of record-setting rainfall. Though the pace of precipitation has slackened this summer, visible impacts are lingering: Along with the resurgence of the dead zone, there was an extreme drop in salinity that is only just beginning to reverse, and possibly losses of underwater grasses, too.
All of those ecological imbalances add stress on species already challenged by poor water quality, overfishing and climate change.
Bruce Michael, a director at the Maryland Department of Natural Resources who measures the dead zone, said, “It’s a stressful time for a lot of our fish species.”
“It’s a stressful time for a lot of our fish species.”
Bruce Michael, a director at the Maryland Department of Natural Resources
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Since flooding rains began in the late spring of 2018, continuing into early this year, scientists and environmentalists have been expressing fears of a hit to the bay’s comeback. They’re still holding hopes that the ecosystem has built up the resilience to weather the extreme precipitation.
Tommy Crowder, a St. Mary’s County waterman, said that while the dead zone is more severe than usual this year, it’s just the latest in a series of swings the bay has always endured.
“Some years it’s less prevalent, and some years it’s really prevalent, and this is just one of those years,” he said.
But some scientists say that as climate change presents more frequent and extreme challenges to Chesapeake, it’s harder to predict how that could affect its recovery. There could be more episodes of unprecedented rainfall, with consequences like those the bay is currently enduring.
“Whether or not it’s a short-term hit or something that’s going to have a legacy beyond this year I think is uncertain,” said Jeremy Testa, an associate professor at the University of Maryland Center for Environmental Science.
The dead zone is an area of water containing little or no dissolved oxygen, which fish and shellfish need to breathe. It can be found every summer, trapped in the bay’s deepest waters from around the Bay Bridge south to the mouth of the Potomac. It’s largest down the bay’s main stem, but also creeps into deeper channels of the Choptank, Potomac and other tributaries.
The dead zone is the product of a domino effect that begins with winter and spring rain, washing fertilizers, sewage and even air pollution into waterways. Those nutrients spur blooms of algae that steal sunlight from aquatic grasses growing at the bottom. And when the algae die and sink, the decomposition process uses up oxygen stored in the water.
This summer, conditions have made the problem especially pronounced.
On the heels of record 2018 precipitation, winter and spring rain acted like gasoline, loading the bay with nutrients that cause algae to blossom. Then, hot summer weather served as a match, helping all that dead plant material to rot even faster. There haven’t been enough storms and strong winds to mix the bay up and allow freshly oxygenated water to reach the bottom.
Estimates of the dead zone’s size in July and early August show that it peaked at more than 2 cubic miles of water this summer — nearly 50 percent larger than the long-term average. That ranks it as one of the three or four largest on record since surveys began in 1985.
In many parts of the bay, the summer heat also means water close to the surface is too warm for many fish. With inhospitable conditions near the surface and along the bottom, it can be hard for creatures to find a home.
“There’s really only a fine layer of suitable habitat for fish,” said Bruce Michael, a director at the Maryland Department of Natural Resources who measures the dead zone. “It’s a stressful time for a lot of our fish species.”
On top of that are other lingering symptoms of 2018′s record rain, which nearly doubled normal annual precipitation with nearly 72 inches at BWI Marshall Airport. Plant and animal species around the bay are suited to tolerate a range of salinity, but for the past year waters have been too fresh for many of them to survive.
It’s too early to know the impact in detail, but anecdotally, the results of all that rain have been devastating for oysters and clams and some types of grasses.
North of the Bay Bridge, there have been reports of oysters killed by low salinity. And around much of the bay, water has only recently become salty enough to plant lab-grown larvae on wild oyster beds with any hope they will survive. The unusually fresh water has also allowed invasive blue catfish — voracious eaters of oysters, juvenile crabs and anything else they can find — to spread.
Grasses had to weather a surge of rainwater that scoured some beds, and also carried with it smothering sediment that blocked out sunlight. Early indications from bay-wide grass surveys this summer suggest those challenges hit some species hard, while others that thrive in freshwater conditions are standing strong, said Brooke Landry, a natural resources biologist at the Maryland Department of Natural Resources.
“We have gotten to a point of resilience in at least a lot of the areas of the bay,” she said. “It doesn’t mean they can withstand anything you give them.”
The bay will survive its latest struggles, said Beth McGee, director of science and agricultural policy at the Chesapeake Bay Foundation. But there will be more to come, and that concerns her.
“What pops up in my head is climate change,” McGee said. If there are more severe storms and more intense rainfall in the future, the low oxygen and low salinity in the Chesapeake this year “could portend our future.”
What can be done? The health of the bay is, to a large degree, a function of the weather. That’s why bay advocates say more must be done to reduce the load of nutrients spread across farm fields or released from sewage treatment plants, efforts required under a multistate bay pollution “diet” that carries a 2025 deadline.
Pierce, the Rock Hall waterman, said he fears it’s too late. With so much population growth and development within the bay watershed, the human impact on the estuary is simply too large. As much as environmentalists cheer progress at cleaning up the Chesapeake, water quality still, in Pierce’s words, “sucks.”
He was barely able to outrun the bad water as he moved his crabbing operation gradually from Virginia to Crisfield and back up to Kent County. He started noticing it in the southern Chesapeake as early as May, and has been gradually moving north trying to avoid it in the months since.
His crew has finally escaped it in waters around the Sassafras River in the upper reaches of the bay. He sees the dead zone as one of countless variables watermen must mind: Stay ahead of it, and you’ll be successful.