Despite the hot weather that has slowed most freshwater fishing, the Potomac consistently has been producing good catches of smallmouth bass with bluegills and catfish thrown in.

The bass range up to three pounds, but to get a good stringer you can't just go anywhere at any time and use any lure. You must consider that the Potomac is low, clear and warm throughout most of the day.

The most productive water has been from Brunswick upsteam to Harper's Ferry. Early morning is best, though some surface feeding often renews at sunset and continues well into dark. The water is cooler then; like people, fish turn off on food when they get too hot.

"If you're on the river by 5 a.m. you can have a ball," said Milt McCarthy, who is studying fisheries management at the University of Maryland. Early this week, McCarthy and two fishing buddies caught and released in two hours more than 20 fish. They kept one 3 3/8-pound bronze-backed smallmouth.

McCarthy was fishing a mile below Harper's Ferry, about a quarter mile upstream from the U.S. 340 bridge. At first the bass were feeding close to the surface. Two-inch rebels, rapals and streamer flies worked will. The most productive streamer fly was the muddler minnow.

After half an hour of vigorous feeding near the surface, the fish retired to the deeper holes and runs. But because of low water, these were only about four feet deep. McCarthy exchanged his fly rod for an ultralight spinning outfit and found more success with a "Mirrow Lure," which is a broken-back diving plug.

By 7:30 a.m. when most people were just arriving, the fish had quit and McCarthy and his friends were heading home.

While minnow imitations work best in the morning, the evening rise is to "white flies." Many trout fisherman will recognize this quatic insect as the reowned white fly that hatches in August on Pennsylvania's Yellow Breeches Creek. Like the trout in the Yello Breeches, Potomac River bronzebacks just dimple the surface as they take the floating insects, which must dry their wings before they can fly. A good imitation of the white fly is tied on a No. 12 dry fly hook.

Low water has actually contributed to the good fishing. The fish congregate in the holes and deeper runs and since the river is easily waded, no fish are inaccessible.

The Potomac should provide excellent fishing for the rest of the summer and reach a peak in the fall. The white fly will continue until September. Minnow imitations, whether for fly or spinning rod, should continue to work well. In October and November a handful of surface poppers and a fly rod will wreak havoc on the old bronzebacks.