The search continued yesterday for an Oakton, Va., man who disappeared Saturday afternoon while canoeing with his 11-year-old son on the Potomac about one mile above Great Falls.

Parmely M. Daniels, 45, a Navy consultant and father of three, was apparently attempting to turn his small, borrowed canoe away from a hazardous, low-water dam north of Great Falls when the canoe headed backwards over the dam, spilling Daniels and his son, Michael, into the river, a Park Service spokesman said yesterday. Michael Daniels was swept onto a rocky island, where he was rescued, but his father, now listed by authorities as a "probable fatality," has not been found.

The incident was one of several on or along the river Saturday. "This was a bad weekend," Great Falls Park supervisory ranger Brian Adams said yesterday.

In another accident Saturday, Alton Montgomery, 39, of Southeast Washington, drowned in the Potomac after falling off the river bank in Georgetown while fishing.

Boats and helicopters from Montgomery and Fairfax counties joined U.S. Park Police as they searched the water and shoreline yesterday for Daniels. Adams said the search would continue twice a day until the body is recovered.

Adams said fast-moving currents, unexpected turbulence below the surface and low dams that must be portaged around are all potential hazards for canoeists. "You can't just get in and start paddling," he said. "If you're going to canoe the river, look at a map, and don't push your skill level. Wear your life preserver, and always let someone know where you plan to paddle."

Robert Hayes, 18, of Beltsville, was listed in critical condition yesterday at Suburban Hospital after a 35-foot fall from a rocky ledge near Great Falls on Saturday. Hayes, a senior at High Point High School, was climbing with friends along a rocky park path known to climbers as the "Billygoat Trail." He shattered one foot, smashed the heel of the other and broke his back in two places.

Lisa DiBiase, 16, of Silver Spring, was luckier. While climbing rocks along the Potomac near Great Falls Saturday she lost her footing and fell 72 feet into ankle-deep, rock-strewn water. DiBiase sustained only scratches and bruises.

"I just kept falling and falling," she said yesterday. "I thought I was going to die. It was like a nightmare, like when they show a fall in a movie, in slow motion. I remember I kept trying to grab onto branches and I kept hitting rocks. When I finally landed, it was on my butt, and it hurt. I thought I'd killed myself. I guess I'm just lucky I didn't land on my head."