Twenty years ago, a movie called "The Endless Summer" chronicled the adventures of two guys who took off with their surfboards to search the world for the perfect wave.

Little did they know the perfect wave was right here in the Potomac River, a few hundred yards below Great Falls at a place called Rocky Island.

Better still, the Rocky Island wave never moves. "You've got a slanted rock shelf down on the bottom," said Rob Saunders of Washington, one of two dozen kayakers out surfing Rocky Island in the cold Wednesday. "The river constricts here. The water rides right down the shelf and when it comes to the end, it pushes up into that standing wave."

Washington-area kayakers flock to ride the wave in spring, summer and fall. Whenever the water level is right, they put on a show for tourists and weekend picnickers at Virginia's Great Falls Park.

But who knew they were out here in deadest winter?

According to Jim Scott, who helped organize the Canoe Cruisers Association's seventh annual New Year's Day Surfing Party, the fun only stops when the river turns to ice.

Scott pulled his red kayak over to shore Wednesday, grabbed hold of an ice-encrusted clump of rocks and held forth on what exactly it takes to join this band of holiday merrymakers. To wit:

At least two layers of polypropylene long underwear, a full dry suit, wetsuit booties with wool socks, a paddling jacket, paddling pants, a swimming cap, wool hat, helmet, life jacket, nylon "pogies" for the hands, Vaseline on any exposed skin and a spray skirt to keep water out of the boat.

"It's a very gear-intensive sport," chimed in Bob Korn, who at age 43 ought to have more sense than to bob around in thundering, 34-degree water in a 20-pound boat. So what keeps him coming?

"This here's my two beers after work," said Korn, a CIA employe who lives in Great Falls, Va. "I stop by whenever the water level and the weather are right."

And what constitutes right? "When it's not frozen or dark out," said Korn.

The way a kayaker rides a wave is similar to the way a surfer rides one, except that the kayaker pretty much stays put while the standing wave swirls and crashes around him.

Potomac paddlers tackle the Rocky Island wave one at a time, lining up in smooth eddy water along the bank to await their turns.

When it comes your turn, you go like mad to get on top of the wave, fighting the water as it shoots through the gorge at about 15 mph. Sometimes you miss and get blown downstream.

But once over the crest, pointing upstream with the nose of the boat buried in the trough of the wave, you can attain a nirvana-like state where the water is racing along underneath the boat at about the same speed as the kayak is shooting down the face of the wave.

This is sheer glory, with the wave curling over your helmet behind you and the trough churning and crashing under and around the bow. It's noise, energy and cold, incredible power all in the grasp of one frail person and a tiny, fragile boat.

When a paddler hits it right, the folks on shore whoop and holler in his behalf. On Wednesday, many of the whoopers and hollerers were girlfriends and wives, and not a woman was in the water. So why weren't they sharing the glory?

"I gave it up a couple of weeks ago," said Cathy Weil. "I put on silk socks, wool socks and neoprene booties. Three layers, and I still couldn't feel my feet three minutes after I hit the water."

Weil said her partners came out of the water that day "looking like glazed donuts. That was it for me."

When the surfing party started just after noon Wednesday, the winter sun was beaming up from its midday perch in the southern sky. It wasn't warm, by any means, but it took a little bite out of the wind. By 3 p.m., the sun was fast disappearing behind the cold, gray rock walls of Mather Gorge. Paddlers began coming in. They would climb out of their boats and crash to the ground.

"Wow," said Eric Lindberg, whose boat was so small he couldn't fit his feet in with more than a pair of socks on. "I've got some amazing cramps."

This being a surfing party, I expected somebody at this point to bring out the Budweiser and start a nice bonfire, but kayaks are too small to carry Budweiser and too wet to keep matches in. The closest anyone came was Scott, who extracted a tiny thermos of tea from his kayak. When he poured a cup, Randy Green slid over and stared, transfixed, until Scott offered him a sip.

"I don't need anything to drink," replied Green with a shiver. "Can I just hold the cup for a minute?"

Endless summer, indeed.

Winter kayaking is for experts only. Nonexperts can stay in shape or learn the basics at indoor rolling sessions this winter, Sundays from 9 a.m. to noon at the Silver Spring YMCA and Sundays from 10 a.m. to noon at Reston Community Center.