The Jug Bay Natural Area on the Patuxent River in Prince George’s County. (Rita Zeidner/FTWP)

As suburban Maryland’s water utility considers how to reduce sediment and pollutants in its two Patuxent River reservoirs, an outside expert has concluded that decades-old horse trails should be moved farther from the water and unauthorized shoreline fishing areas should be closed.

People who use the reservoirs as lakes for boating also should be required to sign affidavits promising not to use their boats in other waterways, the consultant said in a report to the Washington Suburban Sanitary Commission. Doing so, the analysis said, would help ward off invasive species, such as zebra mussels, that can damage intake pipes at water treatment plants.

The findings from a one-year study by EA Engineering, Science and Technology, based in Baltimore County, were released this week as WSSC considers how much access horseback riders, fishing enthusiasts, kayakers and picnickers should retain to WSSC’s 5,600 acres of woods and shoreline.

“Without question, water safety and water quality are our top priority,” WSSC General Manager Jerry N. Johnson said in an interview. “To the extent we can accommodate recreational uses in the area, then we certainly want to do that.”

The Rocky Gorge Reservoir, which straddles eastern Montgomery County and northwestern Prince George’s, and the Triadelphia Reservoir in Montgomery and Howard counties, provide drinking water for about 600,000 people in Montgomery and Prince George’s. Drinking water for the other 1.2 million people served by WSSC in both counties comes from the Potomac River, but the utility does not own or control the land around those reservoirs.

WSSC officials have said that the utility has encouraged recreation on its land since the 1970s through permits ranging in price from $5 daily to $60 annually. The utility has issued about 5,600 recreational permits this year, officials said.

The issue heated up in May 2011, when the WSSC suddenly forbade riding on equestrian trails at Rocky Gorge and prohibited all riding between Nov. 15 and April 1. Horseback riding has not been permitted at the Triadelphia reservoir since 1960, a WSSC spokesman said. Riding at Rocky Gorge is permitted only on a 10-mile stretch of a perimeter road, but riders have said that the steep, deeply rutted road is dangerous.

WSSC officials have said that they had become increasingly concerned that horse waste and sediment running off the equestrian trails made the drinking water more difficult to treat. After objections from the local horse community, the WSSC commissioned the broader $225,000 study of all recreational uses. Johnson said he plans to issue new regulations by early March and that the WSSC’s board has approved $500,000 to carry out changes.

Several people who use the reservoir and its shores say the large swath of woods and beautiful lake vistas provide a rare natural respite in Washington’s densely developed suburbs. About 22 horse stables in Laurel and Burtonsville depend on the Rocky Gorge equestrian trails, riders said.

Ronald MacNab, who represents recreational riders on the Maryland Horse Industry Board, said the equestrian community felt vindicated that the consultant found that their trails caused significantly less sediment runoff than the road that WSSC has required them to use.

Riders have an interest in minimizing sediment and pollution, MacNab said.

“It’s our water, too,” said MacNab, who lives in Colesville. “We drink it, so we don’t want to be the cause of the problem, and we certainly want to be part of any solution.”

MacNab said riders would like to serve as voluntary mounted patrols and have agreed that parts of the trail need to be moved farther from the shoreline.

In addition to closing off unauthorized fishing areas to restore sensitive shoreline, the consultant recommended that the WSSC continue to forbid fishing between Nov. 15 and April 1, when the ground is most vulnerable to erosion.

Mike Thron of Olney, who runs The Maryland Angler’s Network Web site, said he catches bass and crappies at the Triadelphia reservoir. Thron, who said he hadn’t seen the consultant’s report, said the fishing permit that WSSC requires already discourages many people from fishing there.

“They seem pretty stringent to begin with,” Thron said.

The study also found that the recreational areas needed more trash cans and that the perimeter road needed to be improved to allow emergency vehicles, particularly fire trucks, to get in. It also recommended that managed deer hunts continue.

Fred Tutman of the nonprofit Patuxent Riverkeeper organization, which advocates for the river’s water quality, called WSSC’s closer look at the potential recreational effects “long overdue.”

“It’s a beleaguered river system, so anything that takes some of the stress off that water system is a good thing,” Tutman said. “This is not a horse preserve. This is a water preserve. That is really its main reason for being.”