People have rediscovered rivers as sources of recreation. That's good, sometimes, and sometimes bad.

Last weekend river recreation for are paddlers ran from high sport to tragedy. A river is neither cruel nor forgiving. We learn from it. Sometimes the cost is terrible.

On the Potomac two men lost their lives when a canoe went over Brookmont Dan above Little Falls. At certain water levels the dam, five miles above Washington, looks harmless. It's not harmless, ever. At the foot of the dam millions of gallons of water are constantly churning in what paddlers call a hydraulic.

The hydraulic draws whatever flows near into a tremendously forceful underwater swirl that spans the entire river. The hydraulic captured the paddlers. Rescue efforts were futile.

The Shenandoah River above Harpers Ferry was running at 4.2 feet on the Millville gauge Sunday, meaning the level was a little higher than normal after thunderstorms, but still reasonably safe for paddlers who had some idea what they were doing.

I counted myself in the "some-idea-what-he's doing" category, but when my wife and I tackled Bull Falls, where the water shoots through eight-foot-wide sluices in a rock ledge, we went through on our backs, listening to a shattering "crack!" as our swamped boat snapped in half ahead of us.

No one was hurt, though the potential for serious injury was high.

A boat is just a hunk of tin; it's impossible to compare an accident in which a boat is smashed with one in which lives are lost. But the lesson is the same, and it's this: It's almost impossible to overestimate the destructive power of a river. The Potomac above Washington is a beautiful, cool, inviting place to explore in a little boat. So is the Shenandoah. So are Goose Creek and the Monocacy and the Rappahanock. But any of them can be perilous beyond the novice's imagination, and they must be approached with respect.

I have paddled several times with a guy for whom canoeing is a regular pastime. He's serious, but not grave. Last year for fun we paddled Rock Creek during mild high water. I considered it a laugher and was surprised when he gave each potential trouble spot the careful analysis he used on the big river.

Why? Because fast water can pin you and kill you just as quickly on a little creek as on a big river. He did right.

As more people buy, rent or borrow canoes and kayaks to enjoy inexpensive, rewarding recreation close to home, the safety lessons that should precede any river voyage become more vital if injuries and deaths are to be avoided.

The Canoe Cruisers Association, Washington's huge, excellent canoeing club, offers a whitewater course that anyone tackling big water should take. Knowing that some people won't, we offer these simple hints for safe paddling:

LIFEJACKETS should be worn at all times. This is no joke. No serious canoeist or kayaker enters even the mildest whitewater stream without a flotation jacket.

KNEEL and stay low in the boat when in rapids. Inexperienced people who insist on sitting are guaranteed to dump in white water.

STAY UPSTREAM of your boat if it capsizes. If you're downstream of a swamped boat, get away from it. A boat full of water can pin you against a rock and it'll take strong people to free you.

LEAN DOWNSTREAM if your boat is afloat but pinned against a rock or other obstacle. This feels unnatural but permits the current to flow under under the boat and keep you afloat. If you lean upstream (away from the obstacle) your gunwale will dip under water and the boat will swamp.

AVOID TREES, fences, etc. in the water. These are called strainers. If you're pinned against one, the current sweeping through will hold you there until someone pulls you off. If you're pinned underwater, no one will pull you off until you're found, which may well be too late.

FLOAT on your back, feet-first, if you capsize in rapids and are being swept through. Fend off rocks with your heels. If you float head-first you will smack things with your cranium. If you float feet-first on your belly you can't breathe.

FOLLOW SOMEONE who knows the river when you do a stretch for the first time. If you can't find a guide, get someone to describe the likely perils before you push off.

STOP & SCOUT from shore if you are approaching any rapids you have not run before. The worst drops (like Brookmont Dam) sometimes seem the least treacherous. You can spot such a severe drop even if there's no white water associated with it -- the waterline will be level above it and will simply disappear below it. If the waterline disappears, watch out.

RUN STRAIGHT. A canoe or kayak is just as happy going backward as forward; it breaks in two, as at Bull Falls, when it runs through rapids sideways.

DON'T PADDLE ALONE. You may need help.

KNOW THE RIVER, and if you don't know it, get a book. There are a number of river guides available at Hudson Bay Outfitters, Appalachian Outfitters and other outdoor supply stores. The books tell what safe water levels for running a river are. You simply call 899-3210 and find out the current level, as reported from various stations on all the area rivers. If the level is above five feet at Little Falls, the Potomac is considered safe.