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Record rainfall washed 260 million gallons of sewage contamination into Baltimore waterways in 2018. But during dry weather, much of the harbor was technically safe for swimming in 2018, an annual report says.

The annual Harbor Heartbeat assessment, based on routine water samples collected across the Patapsco River and its tributaries, found that bacteria levels improved along much of Baltimore’s waterfront last year. From the Inner Harbor to Canton to Fort McHenry, and in the river’s Middle Branch, waters were safe for swimming in 80% to 100% of samples collected.

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But missing from the data were observations taken during the wettest weather, when it was unsafe for scientists to collect samples by boat — and when the harbor is typically at its most foul. Last year’s record-setting deluge of rainwater also might have diluted the massive surge of pollution, according to the report from the Waterfront Partnership of Baltimore’s Healthy Harbor Initiative.

Fecal matter still made many sections of the Gwynns Falls stream system in western Baltimore and Baltimore County unsafe for contact most of the time. The Jones Falls, the other main Patapsco tributary, experienced increased bacteria levels in many spots last year but remained safe for swimming at least 60% of the time.

Water quality advocates said the results should be interpreted with caution but suggest ongoing city projects to repair and replace aged sewer pipes is helping to clean the harbor.

“We’re really hopeful and encouraged,” said Angela Haren, the Baltimore Harbor Waterkeeper. “We really need more data that is more representative of the different weather conditions before we can make that conclusion.”

The report’s authors emphasized that even though bacteria levels might have declined in some areas, state environment and health officials recommend avoiding contact with urban waterways during and after any rainfall.

More than 71 inches of rain fell in 2018, almost 10 inches more than in what is now Baltimore’s second-wettest year on record, 2003. Typical annual rainfall in Baltimore is about 42 inches.

Rainfall routinely inundates Baltimore’s sewer system through cracks and breaks, overwhelming its century-old pipes and causing backups that overflow into waterways.

In 2017, a drier-than-normal year, such overflows sent about 20 million gallons of sewage-tainted stormwater into city waterways. That contamination increased 13-fold in 2018.

Scientists believe the "long-term trajectory of Chesapeake Bay health is still positive."

That made the report’s results somewhat confusing to water quality advocates, who expected the harbor’s scores to take a hit because of the surge in pollution.

The report’s authors theorized that the rainfall was so excessive, it increased sewage overflows but also watered them down.

“Experts are not certain why bacteria scores remained steady given the overflows, but some think the large quantity of rain may have significantly diluted the stormwater and sewage,” the report says.

Scientists at Blue Water Baltimore, who collected the data but were not involved in the writing of the Healthy Harbor Initiative’s report, said it was unclear whether that dilution meant the sewage pollution was any less harmful to the ecosystem.

But the data at least suggests that the rain likely flushed large blooms of algae out of the harbor, they said. That plant life can block sunlight from reaching underwater habitats, and when it dies, can create dead zones of little or no oxygen in the water.

It was safe to jump into waters off of Fort McHenry almost 90 percent of the time in 2016, but the Baltimore harbor is still far from meeting a goal of becoming "swimmable and fishable" by 2020, according to a report card being released Monday.

The Healthy Harbor Initiative has issued its report since 2014, tied to a goal of making Baltimore’s harbor “swimmable and fishable” by 2020. Most waterways posted failing grades for overall health, scoring no higher than C-minus from 2014 through 2016.

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Last year, it revised the report to no longer issue letter grades for the harbor’s progress toward that goal, and instead to simply focus on “leading” indicators of waterway health that advocates hope will contribute to ecosystem improvements. The 2017 Harbor Heartbeat report found improvements that shocked scientists.

Adam Lindquist, the Healthy Harbor Initiative’s director, said it’s still difficult to declare a trend of improving harbor water quality. But he said the improved results, at least during dry weather, suggest that less sewage is leaking through cracked and broken pipes.

To better gauge water quality going forward, Blue Water Baltimore has installed six bacteria monitors around the harbor at popular sites for kayaking and dragon boat racing, including the Inner Harbor and the Canton waterfront. Haren urged people to visit https://baltimorewaterwatch.org/ to check bacteria levels before heading out into the harbor for recreation.

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