At Melvin Hazen Run, a thin Rock Creek feeder stream off Connecticut Avenue in Northwest Washington, Bill Sittig is on the lookout for poop.

Deer poop. Canada goose poop. Sewage runoff, as well as industrial runoff and other pollutants. All the yucky, invisible bacteria that can find its way into one of the nation’s largest urban national parks after a rainstorm — a rainstorm much like the one that pummeled the city the night before.

Sittig, a former Library of Congress employee who volunteers for the nonprofit Anacostia Riverkeeper, is awash in rubber gloves, sample bottles and a thermometer he pulls from a cooler. He descends through underbrush to the muddy shores of the Melvin Hazen Run, gets his samples and emerges with water that subsequent testing showed was teeming with bacteria.

“I didn’t fall in, but my feet got wet,” he said. “I’m still alive.”

Sittig, 77, is one of 120 Anacostia Riverkeeper volunteers tasked with monitoring water quality in the Potomac and Anacostia rivers, as well as Rock Creek. Partly funded by a $140,000 grant from the D.C. Department of Energy and Environment (DOEE), the nonprofit started scrutinizing bacteria levels and other water quality indicators at 22 sites in May, joining other agencies that monitor the health of the watershed.

The results surprised water-watchers. They found that the Anacostia River, despite its reputation, is cleaner than many people think, and Rock Creek, where children wade, is often really filthy.

“Rock Creek is dirtiest in terms of bacteria,” said Robbie O’Donnell, a project coordinator for Anacostia Riverkeeper, which began monitoring its namesake river before expanding to include the city’s three largest waterways. “It’s one of the biggest polluted areas in D.C.”

Weekly test results released Thursday showed that most test sites — including those on the Potomac and Anacostia — failed, perhaps because of recent rain. But all eight Rock Creek sites failed, and fail more consistently, O’Donnell said. DCist was first to report on Rock Creek’s repeated test failures.

Melvin Hazen Run, for example, registered a bacteria level of more than 2,400 MPN per 100 milliliters — that’s the “most probable number” of colony-forming units per sample. Or, as O’Donnell put it: “Basically how much bacteria is in that 100-milliliter sample we collect.”

To pass the test, Melvin Hazen Run would have had to score no more than 126 MPN per 100 milliliters. Around 2,400 MPN is the limit of Riverkeeper’s bacteria test — a number 19 times higher than what’s needed to pass.

“Values could potentially be higher,” O’Donnell said. “Yeah, they’re not great.”

Three Rock Creek sites also failed pH tests, proving too acidic or too alkaline, and two failed turbidity tests, which measures the clarity of a water sample, O’Donnell said.

Rock Creek’s persistent yuckiness is partly an infrastructure problem.

A $2.7 billion project scheduled for completion in 2023 is limiting runoff to the Potomac and Anacostia, routing it to the Blue Plains wastewater treatment plant in Southwest Washington through 18 miles of four underground tunnels before entering the Potomac.

One tunnel, which started operating in 2018, already is showing results. Though swimming in D.C. rivers is banned, officials began allowing permitted swim events in the Potomac in 2012 and the Anacostia last year (though none have been held). The Anacostia also passed an annual health-check from the Anacostia Watershed Society — earning a “D” — for the first time last year.

The plan to build a similar tunnel for Rock Creek — which would have directed wastewater to the Blue Plains facility for treatment — was changed about three years ago. Instead, officials decided on a “green infrastructure plan” to bring green roofs, porous pavement and rain gardens to the area to limit runoff.

“The updated plan will provide water quality improvements sooner, offer additional environmental benefits, improve affordability, and support local jobs,” an explanation of the plan from D.C. Water said.

Though it’s too soon to know, officials are trying to determine whether the efforts are sufficient to combat pollution in Rock Creek, which is downstream from suburban Maryland.

“I don’t know exactly how effective it’s been,” O’Donnell said. “Some are working. How they’re working in Rock Creek remains to be seen because obviously it’s still dirty.”

John Cassidy, the Clean Rivers Project program manager at D.C. Water, said it’s not clear that a tunnel, or “gray infrastructure,” would be more effective than the “green” program already begun. The costs of both programs were estimated to be about the same, he said, and the agency is studying the effect of green improvements to see whether it makes sense to switch back to a tunnel.

“Green infrastructure offers the opportunity for other community benefits that building a sewer pipe does not,” he said.

Whether improvements end up being green or gray, officials say Rock Creek’s health can improve. Regular tests help to identify trouble spots in waterways. Then, armed with results, officials can find construction projects that need to contain runoff, for example, or pinpoint problems that might contribute to failing grades.

Efeturi Oghenekaro, an environmental protection specialist with DOEE, called the volunteer program a “high priority.”

“We want them to have high-quality data,” she said. “With this, we can identify issues with pollution. We can investigate.”

Normanstone Run, another Rock Creek feeder near the U.S. Naval Observatory with an off-the-charts bacteria count, is a good area for such an investigation, said DOEE spokesman Jeffrey Seltzer. With further study, officials can determine the source of bacteria in the creek, whether construction, businesses or an aging sewage system.

He said Anacostia Riverkeeper’s “citizen science” program helps his agency direct its resources.

“It’s a valuable tool for us to help us focus our efforts,” Seltzer said. “We will try to do just that.”

An hour after Sittig finished at Melvin Hazen, fellow volunteers Stacy Janes and Sara Robinson tiptoed into Normanstone Run. The testing spot, where a tree was tagged with a biodegradable orange ribbon, was hard to locate, but they found it, stepping out of the stream with their sample kit a few minutes later.

“It’s amazing that the watershed wouldn’t be clean enough to use recreationally,” Janes said. “We’re doing anything we can do to aid that process.”