Summer proclaims itself to the water society with a jolt and a clatter. Rebecca Birch and her husband, Rick Rocchio, and his son, Steven, lurch and stagger into walls. Bottles topple, cans collide. Closets fly open, clothes fly out. Bath towels fall on the baby's head. And the aspic,e explodes all over the fridge.

Then Birch and a dozen or so equally rattled neighbors at Pier 7 Marina in Edgewater, Md., where she and her family live aboard a 38- foot fiberglass sloop, gallop madly to the end of the dock, shout curses and shake their fists at whatever hefty cabin cruiser happens to be churning up the year's first monster wake in the middle of the South River.

"Those jackasses," Rocchio mutters on the deck of his boat, A Different Drummer --and summertime on the water has officially begun.

"We're like a groundhog community," Rocchio says, lounging in tennis shorts and nothing else. "As soon as it's nice weather, all the heads pop out of the hatches." Then a sudden and riotous onslaught shatters the peace of the floating neighborhood, a social scene at the water's edge that springs up in full cry.

The river froths to life as the heat comes on, with formerly landlocked Washington urbanites fleeing dry reality in Sunfish, sailboards, Hobiecats, houseboats, Boston whalers, yachts, dinghies, jetboats, jetskis: a maelstrom of floating, skimming, chugging, whirring conveyances.

The banks bustle, too, with a scantily clad menagerie of boaters, anglers, sun-worshipers, landlubbers, rubberneckers, chicken-neckers, river rats, dreamers--while the high school girl who runs the gasoline dock applies "Orchids and You" to her nails.

The party thrives in mid- June and dies about four months later. Not just on the South River, but on the Severn, too, and every other wet inch from the Patuxent to the Potomac, and every plank and pier of the Chesapeake region. The water, once forbidding, has suddenly become a tease, and only the staunchest Oklahoman could resist its simple charm.

In Annapolis, where one bakery cuts cookies in the shape of Izod alligators, the sailing crowd gathers on the afterdeck of Carrol's Creek Caf,e, across Spa Creek from the Annapolis Yacht Club, to cheer the finish of the club's Wednesday night races. It's an attack of khakis, greens and mauves both local and foreign, with the interloping tourists present concerned largely with their daiquiris. The serious sailors repair to Marmaduke's to watch videotapes of the racing battle.

Up and down the waterfront from Annapolis to Anacostia, masts are hoisted, hulls scraped, brass fittings polished, cobwebs wiped away and any number of bilge pumps removed and replaced. "The sunshine crowd says, 'Let's use the boat this weekend,' but they have no idea if it it'll actually run," says a wiry marine parts supplier named Pat O'Hara, who wanders the Washington part of the Potomac delivering pumps and valves. "In June people are just discovering that their boats don't work."

A sun-bleached woman named Kathy White, who sports a T-shirt reading "Wharf Rat" on an ample frame, says with a hint of mysticism, "I really get into the wood."

She's an expert oyster- shucker during Florida winters, but refinishes wooden boats during the Washington summers, and at the moment she's putting some elbow grease into the Sen. G. W. Pepper, a yacht berthed at Washington's Gangplank Marina on Water Street. "There's a whole different atmosphere on the water from everywhere else I've been. You don't have to be on the defensive all the time. People are friendlier. I think maybe, after this, I'll become a cruise director on a steamship. But what I'd really like to do one day is open up my own raw bar on the river."

In summer the water casts a spell on people, and occasionally the result is madness. At the Washington Sailing Marina on the Virginia side of the Potomac, Anders Gylkenhoff toils renting sailboats but also keeps an eye on the river. "I had to save a man from drowning yesterday," says the golden-maned lad, one pierced lobe sporting a tiny earring. "He drank a little too much and jumped off the dock. That kind of thing is to be expected from now on."

Not far away on a grassy bank, the river has a diffferent effect on Vernella Carr, an Alexandria school bus driver casting her line for catfish. "My mom used to take us kids fishing all the time in Halifax, North Carolina, and it was just very peaceful," she says. "I think that's why I like it here. I can forget about the bus, forget about hauling kids, forget about housework and just sit here. I don't care whether I catch a fish or not."

The temperature rises, and dreamers are drawn helplessly to the slips of Southwest Washington, to gawk at, wave or otherwise pay court to the residents of the Capital Yacht Club and the Gangplank Marina. The yachtsmen are present-day sun kings who, like Louis XIV, perform their daily ablutions more or less in public view, royally protected from hoi polloi by a rail, locked gates and a moat. The iron rail is a great divide, over which common landlubbers hang to stare longingly at the royals, trying every so often to engage them in conversation. "I'm a wall person," says a slight, bearded fellow named James Smith, as he plies passing boat people with offers of cold beer.

"I don't pay much attention to those people anymore," says yachtsman William Hamilton. His 42-foot cruiser, Love Story, is berthed beside the rail, along with such sleek pleasure boats as After Midnight and For Play. "But I know there's a couple of boaters here who do nothing but work the rail, sitting on deck with a cocktail in their hand and whistling at the women going by, trying to get them aboard. Especially Jack the Hook. He watches the wall pretty carefully."

Summer brings pande monium to Washing ton's fish market on

Maine Avenue, where

men with monickers like "Captain Red" and nautical tattoos on their crab- bitten arms stand all day long in barges hawking flounder, grouper, sea trout, haddock, blue eel, bluefish, conch meat, croakers, cherrystone clams, whiting, spot, monkfish, red snapper, salmon steaks, bay scallops, shrimp, octopus, squid, lobster and the occasional frozen frog leg.

But what everyone wants is crabs; the air is hot and heavy with their savory smell.

"Live crabs, come and get 'em while I got 'em, ain't gonna have 'em much longer, crabs, live crabs, have mercy," Eric Wright chants from atop a rickety stepladder, near where men are tossing them spiced by the bushel into big steaming pots.

Jimmy Wray of Clarksburg, Md., totes away half a bushel, the crustaceans scuttling and clacking in a plastic bag. "These females are heavy," marvels the retired District firefighter. "Just look at the eggs hanging off 'em."

Sometimes in the afternoon, a summer storm comes through: an impenetrable mass of clouds sweeping thunderously over the water. The spectacle gives pause to cargo broker David Lee, who conducts business--matching up cargoes to outbound tramp steamers--aboard a sailboat equipped with a computer terminal and three telephones. For a moment he stops sending wheat to Odessa and scrap steel to Yokohama, and goes up on deck to watch.

"It's an awesome display of nature in the raw," he says aboard his boat Ida Mae, not far from National Airport. "You watch the planes skipping in under those thunderheads and you really can see how those pilots earn their pay."

You know," Rick

Spinner says on a

day in late June,

"the water's like a

woman." He's waiting for the tide to drop on the Virginia side of the Potomac, his three Daiwa fishing rods propped against a picnic table. "You can never tell what she'll do next."

Draping a pair of sturdy arms over a tackle box brimming with rubber worms, he adds, "I used to swim back and forth across this river when I was little. I didn't have the money for a swimming pool. The main thing the river means to me is peace of mind. I can fish. I can be content. I'm a nature person, period."

Before long he's in the throes of a dissertation: "When you see a slight budding on the trees, you'll know that the herrings, shad and white perch will be running. When the bloom comes full out, like now, you get the rockfish, and then the papermouth bass. I use the quiet approach: first fish the bottom, then the middle, then the top of the water. It all depends on catching the tide coming in or going out."

"I never did see him catch a thing," chimes in Donald Cameron, a rusty-haired old salt with a Scottish burr as stiff as a 20-knot breeze. He grins a weathered grin and squints, pulling a floppy hat over a burnt and freckled brow. "All I ever see him do is sit here with his tackle box having a beer."

At sundown Pat

O'Hara takes a spin

in a powerboat from

the Fort Washington

Marina in Prince George's County. He steers in the evening haze through Piscataway Creek and into the Potomac, past tree-hidden Indian burial grounds on the Maryland shore. A heron flaps by. A crane standing beside a fallen tree gazes intently down at the water, and finally pokes its head under to swish it about for food.

"I bet you didn't think you'd see something like that just 12 miles out of Washington," O'Hara says, and the boat chugs on.

The river looks lush, almost Amazonian, its shores crammed with vegetation and small buzzing things. The water is still, the sky heavy. A matched pair of swans comes gliding by. A flock of chattering geese promenades along the bank. Kids splash and shout from the rocks of the Fort Washington lighthouse.

O'Hara turns on the running lights as the boat passes Mount Vernon, gleaming pristinely in the middle distance high on George Washington's hill. He heads toward the other side, where a bleached, burnt-out hulk of an 18th-century manor house reflects the summer evening's last bit of light in splendid decay.