We are sliding along the shoreline of a deserted lake. A west wind has picked up, carrying chill air through the deep forest, rustling the dry leaves that are the first signs of a changing season.

It has been a long day, starting before dawn. We have watched the sun rise in clear skies, then seen storm clouds mushroom, only to be blown off by the freshening breeze.

Jim Donald is at the stern, guiding the hushed power of the electric trolling motor, trailing a light rod over his left shoulder. Thirty yards astern, his deep-diving speed shad lure is working through the brush, bumping bottom and crashing in and out of the submerged stumps and branches.

Suddenly the rod tip plunges and stays down. Donald leaps to his feet, nearly upsetting the burdened john boat.Before he can get his hand to the crank, line starts spilling off the little reel. There is something on the other end of the line, something big.

The fish stays deep and fights hard. "I think I've got him by the tail," Donald shouts. For sure, it battles like a foul-hooked bass, but when it comes to the surface, huge mouth agape and shaking a prehistoric head, it is clearly a great northern pike.

"By golly, it's a pike," says Donald. "How big do you think it is."

Donald lays a tape measure to the thrashing beast and pulls out 21 inches of tape. It's a big one all right, a keeper, but after a last admiring glance, Donald eases the pike into the clear water, revives it with a couple of sweeps of the hand and watches it dart off to freedom.

If you could shut off your mind for a moment, you'd think you were in some isolated spot in Northern Quebec. But the trees are wrong - poplars and elms instead of tail pines and maples. You are, in fact, a 25-minute drive from downtown Washington in Rocky Gorge, one of the impoundments that provides drinking water for close-in Maryland.

This is the time of year when the fishing picks up hereabouts, and Rocky Gorge and its sister reservoir. Triadelphia, are good places to try your luck. The day Donald spent on the water, there was only one other boat out all day. It was a peaceful scene.

Donald had provided a little warning before we met in the dark at Scott's Cove, off Colesville Road about halfway up to Columbia. "It's frustrating fishing," he had said.

Indeed, it's not easy to load up the boat at either Triadelphia or Rocky Gorge. But there are some remarkable trophies lurking in the deep water.Last month, a 12-pound 10-ounce pike was landed at Triadelphia. The biggest largemouth bass landed this year was a 7-pound 11-ouncer at Rocky Gorge in April.

Donald is used to long waits between catches. He's the chief unofficial public relations man for the close-in impoundments. "I don't understand why people haul off and go to Lake Anna and Gaston," he has said many times. "There's good fishing right here."

Ke knows the three closest fishing lakes - Burke Lake, Occoquan and Triadelphia/Rocky Gorge - as well as anyone.

He also has his own method for finding the fist. All the lakes limit boats to small outboards or electric trolling motors, so there's no way to race about the pond from one good hole to another.

So while Donald maneuvers from one spot in the next, he employs the old saltwater trolling technique. He heads for the deep water and runs a lure along the bottom. That's how he laced into the big pike.

"It helps you find the fish," he said. "Then you can stick around and cast to them."

Triadelphia and Rocky Gorge are run by the Washington Suburban Sanitary Commission, which sounds worse than it is.The water in both impoundments is "raw," according to WSSC public affairs officer Arthur Brigham. The two dams stop up the flow of the Patuxent River, which is clean enough upstream to support a naturally reproducing trout population.

To fish Triadelphia/Rocky Gorge you need a WSSC permit, which costs $10 a year or $1 a day, including boat-launching facilities. The permits are available at Brighton dam, which is off New Hampshire Avenue about three miles north of Ashton and is open at all hours. Or you can buy one directly from the WSSC offices in Hyattsville during normal working hours.

Our catch for a long day of serious fishing was three bass, two of them keeper size, and two pike, one of which came up and snapped up a Rebel lure right at the boat, then got off before it was landed.

The pike are the real thrillers. They've been stocked for the last four years and are beginning to take hold. The stocked fish come at 12 to 14 inches and it doesn't take them long to achieve 20-inch keeper size. They feed happily off the abundant crappie in the lakes.

With pike, pickerel, largemouth and smallmouth bass plus the inevitable panfish, carp and catfish, you'd think the WSSC would be content.

It's not. Shed manager Paul Hancock is already negotiating with Virginia state officials over the purchase of some striped bass fingerlings. Rocky Gorge rockfish. Sounds great.