Road running in Greenfield began almost 40 years ago with a 10-kilometer race sponsored by Clark’s Sport Shop and organized by Joe Martino, Frank McDonald and the late Jim Allen. At its peak, the Greenfield YMCA Classic was a rite of spring when hundreds of locals hightailed it down Mountain Road through Bingville and along Deerfield Street to Bank Row and up to the YMCA.

The Connecticut River Conservancy similarly dates back to last century when travelers on Route 2 could tell what dye the paper mill was using by looking at the Millers River. Sometimes the water was blue, other times it was red, or green. The Clean Water Act of 1972 changed that, and today New England’s waterways are suitable for fishing, kayaking and other freshwater activities.

“Folks tend to think our work is done but that’s absolutely not the case,” said Angela Chaffee, the Conservancy’s outreach and events director.  “We need to work diligently to keep it clean — in ways from making sure industries stay within their permits to picking up dog waste to not littering.”

On Sunday, Greenfield Community College will do its part by hosting the inaugural New England Green River Marathon. Sponsored by the Conservancy and the venerable Sugarloaf Mountain Athletic Club, the course starts in Marlboro, Vt., and ends near the East Building on the GCC campus. It was mapped out by Tom and Laure (Van den Broeck) Raffensperger, who are club members and outdoor activists.

“Laure and Tom contacted us,” said Chaffee. “They were involved in the Green River cleanup which is part of the source-to-sea cleanup. They thought doing a marathon would help highlight the need to clean up the rivers in our area.”

The field was capped at 363 runners who paid $105 apiece for a souvenir shirt, commemorative medal and bus transportation from the GCC parking lot to the starting line. “We’re raising money to protect, preserve and clean up the river,” said Raffensperger, a Greenfield resident.

Various running clubs have entered — 18 runners from the Sugarloaf Mountain AC, a dozen from New Hampshire’s largest running club, the Gate City Striders, eight from the Berkshire Running Club — together with Team Psycho, Troubled Soles and the Boston Vegan Running Club. 

They’ll be setting their alarm clocks and packing GU for the one-way bus trip to Marlboro College at 5:30 a.m. The race kicks off at 7 a.m. Townsfolk will barely have awoken to see interlopers running down Moss Hollow Road to Green River Road past horse pastures, logging roads, stone walls and maple sugar houses.

The first 10 miles are mostly downhill to Guilford, where the course crosses the covered bridge next to the Timber Crib Dam and turns left onto the shaded, flat and dirt-packed road.

An aid station near Ten Mile Bridge in Leyden will provide medical help. A public access path leads to a swimming hole, one of several spots where shallow rapids spill into deep glistening pools. 

Raffensperger said he expected runners to start crossing the finish line before 9:30 a.m. “We have a lot of folks who will be trying to qualify for the Boston Marathon, and lots of first-time marathoners. They’re going to be in tough shape at that point and if people can get out and cheer, a little encouragement can go a long way. It really makes a difference in those late miles when you wonder what the hell you’re doing.

“Don’t drive on the course,” he added. “I’ve said that a million times. It’s foremost on my mind.”

The Greenfield Police Department will help with traffic, and food and drink will be available for everyone.