If you’ve ever been for a hike in Rock Creek Park after a rainstorm, you probably know the smell.

“It smells like somebody has just flushed directly into the creek,” says Jeanne Braha, executive director of the nonprofit Rock Creek Conservancy. In a sense somebody — or many somebodies — have flushed directly into the creek. Each year, some 50 million gallons of raw sewage, mixed with stormwater, discharge into Rock Creek. It makes the creek inhospitable to aquatic life, and dangerous for humans to wade in.

The source of the sewage problem dates back to the early 20th century, and for the past two decades local officials have been working with regulators at the EPA on a plan to end the pollution. Now, they’ve just completed one of the first projects to stop sewage overflows — but it’s not what you might be thinking: it’s not a bigger sewer tunnel (like the one DC Water built under the Anacostia River). Instead, the water utility is installing dozens of small projects that look like glorified landscaping, in neighborhoods many blocks away from Rock Creek.