PROVIDENCE — Mayors in town for the U.S Conference of Mayors annual summer meeting and volunteers from Citizens Bank built a playground in Olneyville on Sunday afternoon, in an area along the Woonasquatucket River that has come along way from its days as a haven for drug addicts and prostitutes.

The roughly 75 volunteers filled a play area with wood chips while city workers erected a plastic play set with slides and walkways and climbing areas. Other volunteers weeded a community garden, while still others painted and hung up decorations around the park and the nearby river walk.

They also laid down fill to create a path from the main part of the park to a long red shed where volunteers this summer will show young people how to repair bikes.

The total cost of the work was about $25,000, according to Citizens Financial Group CEO Ellen Alemany, whose company is paying for the new play equipment.

Long a work in progress, Riverside Park, on Aleppo Street, is the center of the revitalization of what was once one of the seediest areas on the West Side. The seven-acre green space is the former site of the Riverside Mill, a factory complex that burned in 1989 but whose burned out ruins became a hub of illicit activity.

“You never went down here except for drugs and prostitution,” said Barbara Fields, executive director of Local Initiatives Support Corporation, or LISC, a national organization that has invested in low-income housing in the neighborhood.

But as the mill site and the Woonasquatucket were finally cleaned up, investment gradually returned.

Olneyville Housing Corporation, with the help of LISC, built more than 50 housing units around the park, both rentals and condominiums, in recent years. The state funded the creation of a bike path along the river that now pushes into Johnston, and the city developed the park, which now boasts a community garden, a canoe launch, athletic fields and two playgrounds.

“This wasn’t an area where kids played,” said Kathy O’Donnell, director of public affairs for Citizens Bank, who grew up in the city’s Mount Pleasant neighborhood. “Now the families are back.”

Providence Mayor David N. Cicilline, pushing around a wheelbarrow filled with wood chips, agreed: “This is the most changed neighborhood in the city.”

The service project is an annual rite of the U.S. Conference of Mayors summer meeting, which enters its final day on Monday.

“It’s a good day to give back to the community, to bond with other mayors and see some of the city’s neighborhoods. I’m particularly impressed with the housing projects in this neighborhood,” said Schenectady (N.Y.) Mayor Brian U. Stratton, taking a short break from the work. “We’ve always held this city as a model for reviving a downtown and regrowing neighborhoods.”

pmarcelo@projo.com