Old habits die hard, as we discovered in the rushing riffles of the South Fork of the Shenandoah. Joe Sottosanti and I were fishing for smallmouth bass in waters he knew as well as most of us know our front walks. He'd fished them for 20 years.

The funny thing is that both of us knew we were fishing contaminated water. We knew that the state had decreed a year before that the fish from the South Fork were mercury-poisoned, unfit to eat and illegal to keep.

Yet every time we caught a bass we'd hold it up, admire it while it wiggled and wrestled, them calmly eyeball its length when it settled down.

"Doggone, Joe," I'd say after awhile, "I believe this one's a keeper." "Doggone," Joe would say back, "I think you're right."

Of course, there is no such thing as a keeper bass in the South Fork these days. So after we'd dutifully checked each catch out we returned it to the stream, whether it met the standard 12-inch minimum for Virginia waters or not.

Normally that would be no big deal because we wouldn't catch many "keepers" anyway. In recent years Shenandoah bass have been notable for their lack of size. "It seems like they're all between 10 1/2 and 11 1/2 inches." Sottosanti said as he headed out.

But not this day. In an hour and a half of fishing one of Sottosanti's old favorite haunts we landed better that a dozen fish, at least a third of them in the 14-inch category.

That doesn't sound like much on paper, but a smallmouth that big puts up a whale of a battle, complete with leaps and runs, on ultralight gear. They are as much fun to catch, pound for pound, as any fish that swims.

Maybe we were just lucky. Then again, maybe the South Fork ban is reversing the trend of the last decade and big fish are going to start showing up in numbers again. Putting them back can't hurt the population.

That may be the only silver lining on the cloud of mercury contamination. The Virginia Commission of Game and Inland Fisheries thinks so.

Jim McInteer, assistant director of the commission, said the state is watching closely what happens to the "fish-for-fun-only" South Fork.

"We have a strong feelimg that when you take all the predators out when they are 12 inches (as fishermen presumaly did) you severely affect the nature of the fishery," Mclnteer said.

"We've proved it in ponds, but we've never had a chance to close off agood stream like this before. It should provide some interesting information, but that's about the only plus we see in the whole thing."

Mercury was discovered in the stream bed and the fish of the South Fork last spring. Workers at the duPont plant in Waynesboro made the find the governor banned taking fish on June 3. Indications are that the contamination came from residue of mercury from products that the plant stopped producing in 1950.

Mercury doesn't go away. As Mclnteer put is, "It's not something that degrades in the environment. Once you're stuck with it you're stuck with it. We don't anticipate any change for many years to come."

Intially there was great concern that making the stream fish-for-fun-only would have a devasting effect on the local economy.

Fishing pressure dropped about 28percent immediately, and state officials estimated a loss of about $400,000 to interests along the river from Waynesboro to Front Royal.

That apparently hasn't happened. Jack Hoffman,s director of the state fish division, said fishing pressure has been bouncing back steadily, though it hasn't yet reached pre-ban levels.

There's good reason for the come-back. Even if you can't keep 'em, the South Fork is still a wonderful place to catch 'em.

Sottosanti's technique dates back to the days when he and his family ate Shenandoah fish three or four times a week without ill effects.

That's meat fishing and his methods are tried and proven. He uses minnows that he seines himself at the start of the day, so he's getting the genuine local article.

Sottosanti uses a broad, 10-foot seine with a pole at each end. He finds a grassy, shallow bar along shore and looks for shiners. When he spots them, he puts one man on the shallow bar and takes the other end of the seine out in deeper water.

In three or four swoops he picks up enough fat, bright shiners for half a day's fishing.

These minnows are pierced through the line on tiny hooks, just barely bigger than trout hooks. Scottosanti uses no weight on the line and a four-pound test ultralight rig.

He drifts downdstream in hs canoe, looking for flat water above and below riffles. He tosses the minnow in the deep holes and lets it drift. As often as not a bass can't resist it.

One of the most exciting developments comes when the bass makes its first lunge. The frightened shiner makes valiant leaps out of the water to escape, while the angler stands breathlessly watching big fish leaping after little fish, waiting for the tap that tells they're both attached to hs line.

Take a camera along. The fishing is great, but pictures are the only proof you can take home.