For Maryland boaters planning to set sail on the Chesapeake Bay this summer, flourishing underwater grasses that tangle easily around vessel propellers might seem like a nuisance.

Doug Myers, a senior scientist for the Chesapeake Bay Foundation, wants people to know that the bright green vegetation is actually a sign of a healthier waterway.

“It’s a good problem to have,” Myers said.

A new report this week from top scientists who study the bay estimates that underwater grasses increased about 12% in 2022. Researchers say the approximately 76,462 acres of grass mapped in the bay and its tidal tributaries last year represented a 9% increase over the long-term average taken between 1984 and 2022. Seagrasses, in particular, create a healthy habitat for the region’s emblematic blue crabs.

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The report, produced by the Chesapeake Bay Program, comes on the heels of a similarly positive forecast published in June that predicts the bay’s dead zone — an area low in oxygen that can suffocate marine life and diminish habitats — could shrink by as much as a third this year. If the forecast proves accurate, the Chesapeake Bay could see its smallest dead zone on record this year.

The program, a regional partnership between federal and state authorities, was launched decades ago to improve the bay’s water quality and restore its habitats. Environmental advocacy groups like the Chesapeake Bay Foundation, which is separate from the program, say significant progress has been made since then, but there is still much work to be done. The program recently acknowledged that it will not reach some of its key goals by a 2025 deadline.

Scientists attributed the expanding seagrass acreage and dead zone forecast in part to below-average rainfall and cooler summer temperatures associated with the La Niña climate phenomenon, which features stronger surface winds across the Pacific Ocean and cooler conditions.

“When you have a general overall reduction [in pollution] and the years haven’t been as rainy, that means the ecosystem has an opportunity to repair itself,” said Brooke Landry, a biologist for Maryland’s Department of Natural Resources.

The La Niña cycle ended earlier this year, paving the way for its warmer counterpart, El Niño, to emerge. It’s not immediately clear how El Niño will impact weather in Maryland, which falls into a geographic transition zone. During winter months, southern states could experience wetter and cooler conditions, while northern states face drier and warmer weather.

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Less rainfall in Maryland in recent years meant there was less opportunity for nutrient pollution to wash into the bay’s watershed from farmlands or sewage system infrastructure. Nutrients such as nitrogen and phosphorus feed toxic algae blooms that remove oxygen from the water as they die off or block sunlight that underwater grasses need to survive. A record-breaking surge of rainfall in 2018 and 2019 resulted in a 38% drop in underwater grasses.

Still, recent efforts to reduce nutrient runoff and restore ecosystems have bolstered the bay’s resilience to major storms or hurricanes, Myers said.

“A single storm might set us back, but the bay we have in 2023 is way more ready to accept that kind of event,” he said.

The state’s efforts to curb nutrient runoff have extended to Baltimore City, where regulators have extended supervision of the jurisdiction’s beleaguered Back River Wastewater Treatment Plant.

The state took control last year of the Dundalk-based plant after the city failed to act on multiple permit violations and sewage discharges. Environmental advocates have also filed a federal lawsuit seeking a court order to fix Back River along with the city’s other wastewater treatment plant, Patapsco.

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“Ideally, we’d already have a sewer system that doesn’t have rainfall getting into the sewer system today,” said Alice Volpitta, who directs water quality monitoring programs for the nonprofit Blue Water Baltimore. The nonprofit organization is a plaintiff in the wastewater treatment plant lawsuit.

The seagrass and dead zone reports are “good news,” Volpitta said. Baltimore is reporting a much lower volume of sewage overflows so far this year, though she warned more rainfall could result in an increase.

“If these decreased dead zones are driven by a decrease in rain, that’s still good,” she said. “It’s important to celebrate what we can.”

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