Horseback riders are squaring off against the Washington Suburban Sanitary Commission over a decades-old equestrian trail that the utility says is sending sediment and horse waste into the Maryland suburbs’ drinking-water supply.

The WSSC recently banned horseback riding from a trail on the utility’s land surrounding the Patuxent River’s Rocky Gorge Reservoir, which straddles the border between eastern Montgomery and northwestern Prince George’s counties. The Patuxent provides about 30 percent of the suburbs’ drinking water, and the Potomac River provides the rest.

Horseback riding is now allowed only on an access road on the edge of the WSSC property, a move that WSSC officials say keeps horse waste and any trail dirt in storm-water runoff farther from the reservoir. But horseback riders say the one-lane dirt road has sent far more soil into the streams feeding the Patuxent than their 18-mile, 2-foot-wide trail.

The road’s steep hills and deep ruts, they say, are unpleasant for riders and potentially dangerous for horses.

Many riders say they suspect that the WSSC designed the new rules to discourage riding in the serene, sun-dappled woods. In addition to closing the trail, the WSSC has prohibited riding between Nov. 15 and April 1 and has limited access to eight designated entrances that have limited parking for horse trailers.

“In my mind, the whole thing is a ploy to make riding so untenable and unpleasant that no one will ride,” said Terry Ledley of Laurel. The WSSC named part of the equestrian trail in Ledley’s honor in 1998 to recognize her 20 years as a volunteer in maintaining it.

“I’ve loved it for so many years,” Ledley, 84, said. “To make it unavailable to people, I just don’t understand.”

About 22 horse stables in Laurel and Burtonsville depend on the trail, riders said.

Debby Poole said her husband’s family has been riding the trail for five generations.

She said her horse-boarding business, Belle Cote Farm, which her family has operated in Burtonsville since 1968, is now in jeopardy. Customers, she said, “have all told me if we don’t have the trail, we won’t keep our horses there.”

WSSC spokesman Jim Neustadt said the utility has encouraged the public to use its land and reservoirs for fishing, some boating, picnics and horseback riding since the 1970s. But, he said, horse waste and sediment running off the trail make the reservoir water harder to treat.

“It’s not like we have anything against horseback riders,” Neustadt said. “It’s what we think is best for the watershed and to protect the drinking water for our customers.”

Neustadt said horseback riding has been restricted during the 41 / 2-month period because those months have high rainfall and little vegetation to help absorb water and slow runoff that causes erosion.

The horse community has asked the WSSC’s six politically appointed commissioners to reverse the trail ban that took effect May 15, which was first reported by the Gazette. C

hairman Roscoe M. Moore Jr., a veterinarian and a former assistant U.S. surgeon general, said the commissioners asked WSSC General Manager Jerry N. Johnson last month to provide more details about the ban within 60 days. A commissioner will also tour the trail, Moore said.

“There’s hope the trail might be reopened, given certain restrictions,” Moore said.

“We have a responsibility to maintain the watershed, and the horse community has used these trails for years. We need to get together and work out a resolution.”

Horseback riders say they helped the WSSC for more than 30 years by maintaining the trail, picking up trash and reporting problems — largely illegal campers and dirt-bike riders — that they came across.

They said they were caught off guard when they suddenly began seeing “Stay on trail” signs with arrows pointing to the access road.

The problem, riders say, is that the perimeter road has steep hills compared with the relatively flat trail that zigzags up and down hills more gradually.

The flatter and narrower trail also sends less dirt rushing off into streams after a rainstorm than the wider, steeper road, they said.

On a recent tour of the reservoir’s woods, horse enthusiast Barbara Sollner-Webb said it’s impossible that enough sediment is washing off the trail to affect the drinking-water supply. Even so, she said, riders have offered to move the trail farther from water and help restore eroded areas.

“The few parts where there are problems,” Sollner-Webb said, “the equestrians would love to help fix.”