SAUGUS – Saving a river from the negative impact of urban encroachment isn’t a task for the light-hearted.Twenty years ago, a group of dedicated environmentalists banded together to create the Saugus River Watershed Council (SRWC). Its mission was simple: protect and restore the natural resources of the Saugus River watershed.Today, with 675 members and hundreds of volunteers, the council perseveres in its mission, which includes fund-raising efforts like its annual River Night & Auction. The May 3 event at Spinelli’s banquet hall on Lake Suntaug, Route 1 south in Lynnfield, typically attracts hundreds of people concerned about the health of the Saugus River.According to Joan LeBlanc, executive director of the SRWC,this year’s live and silent auction will include vacation getaways, Boston Red Sox tickets, personal luxuries, home and gardening products, items for children, original artwork, dinner at fine restaurants, tickets to museums, jewelry, and gifts with environmental themes.Proceeds support the council’s education and river restoration programs, she said, noting auction items are still needed. Advertising opportunities in the event program booklet are availableIndividual tickets to River Night are $35 and include dinner as well as admission to the auction.River Night provides guests a fun atmosphere in which to casually dine, socialize, listen to jazz music and browse the auction tables, LeBlanc said.Guests tend to hail from all the communities in the Saugus River watershed, a 47-square mile area of land which drains into a single river.The river headwaters begin at Lake Quannapowitt in Wakefield. After coursing through Wakefield, Saugus and Lynn, the waterway empties into the Runmey Marsh and Pines River estuaries in Revere, Malden and Everett. Eleven communities are part of the watershed, including Lynnfield, Malden, Melrose, Peabody and Stoneham. The Saugus River is 13 miles long, known to Native Americans as Aboutsett or winding stream. It falls 90 feet from its source in Wakefield to where it pours into Broad South beneath the Gen. Edwards Bridge, which divides Lynn from Revere.The Tuesday evening event is from 6-9 p.m.