Over a decade, participation in the Minnehaha Creek Watershed District’s summer cleanup event has skyrocketed, bringing 1,600 volunteers to sites along the 22-mile waterway to pick up 4 tons of debris. And that was last year alone.

But water quality improvement is happening more slowly, said Telly Mamayek, spokeswoman for the district.

In short, the cleanup effort is still very much needed. The water still has too-high levels of phosphorus and chlorides, and some still use the creek as a dumping ground.

On Monday, the district will announce plans for its 10th annual watershed cleanup day on July 24, now one of the Twin Cities’ biggest environmental cleanup events. Recruitment for an expected 2,000 volunteers will begin.

This year, cleanup will be concentrated at three sites: Lake Hiawatha Park in Minneapolis, a spot near the Knollwood Target in St. Louis Park and by the city of Minnetonka’s ice arena, a new location.

Because the refuse collection happens in urban areas, volunteers find a variety of odd items. One year, someone found a gun and police were called, said Brian Shekleton, vice president of the Watershed District’s board.

Participants also recover chunks of canoes, strollers, radiators, bicycles, concrete blocks and wallets, along with the all-too-common beverage containers and bottle caps.

Special recognition is given to the person who recovers the most candy wrappers, said Mamayek, adding that kids especially like to compete for it.

People “have to stoop down and make the effort to really get the small stuff,” she said. “That’s just as harmful as the big stuff.”

The waterway’s pollution stems from stormwater runoff.

“It’s really kind of amazing how many stormwater pipes discharge into the creek,” Shekleton said, citing more than 100 pipes in Minneapolis.

Recent efforts to rehabilitate the creek have gone beyond the one-day cleanup. A patchwork of partnerships among cities, the state, the Watershed District and the Metropolitan Council have paid for the ventures.

Last summer, the creek’s curves were restored and a boardwalk and trail were created in St. Louis Park. The creek had been straightened and dredged more than 70 years ago to make development nearby easier, but that caused flooding and erosion. Adding back the twists and turns should reduce erosion, Mamayek said, and it also should bring back animals.

Another 2015 project reclaimed land near the creek in Hopkins by knocking down dilapidated residential and commercial properties. That made room for more open space along the banks, resulting in more filtering of runoff water before it hits the creek.

The cleanup event not only improves the area in a visible way, it also provides “an education piece,” said Shekleton. “That just pays off in spades.”

Jacqueline Di Giacomo of Tonka Bay has taken part in the cleanup with her kids since 2013. She has earned the status of a master water steward — like a master gardener but with water expertise — through a program offered by the Freshwater Society and the Watershed District.

Di Giacomo initially attended the cleanup day because of her commitment to environmental issues, but now it’s become a family tradition, she said.

“They have it down so it engages all ages, from kids to seniors,” she said. “The kids just went from reluctant to ‘are we signing up again?’ ”