The pristine sands of the Hamptons are regarded as private property by the Manhattan elite. But can the locals win their long-standing battle to stop day trippers from blighting the idyll?

The windswept expanse of dune and beach that stretches 30 miles from Montauk Point to Southampton – known colloquially as the Hamptons – comes with the dual reputation as a summer playground for Manhattan society and a piece of pristine coastline that breaches into clear, cool Atlantic water. From the schools of striped bass to the bizarre, blue-blooded horseshoe crabs and the tiny, intensely-protected piping plover, the Hamptons are rightly celebrated for their natural beauty.

But away from the ocean swell and off the beach, one finds a highly-stratified society where people are dedicated to enforcing their freedom by regulating others. In winter, the Hamptons are desolate and whipped by northerly storms; in summer, the population soars to 100,000, five times its off-season size. Each beach is claimed by a different group: at Montauk, the surfers and sport fishermen congregate; in Amagansett it's families with children; the wealthy cluster in prime multi-million-dollar beachfront properties on Georgica Pond and Further Lane.

On the main roads, though, it doesn't matter: bumper-to-bumper traffic and electricity brown-outs affect everyone equally. Still, the whistle of Learjet engines overhead is a reminder that access to private aviation is a decisive lifestyle advantage.

For many, the Hamptons summer is an employment boon; for others it's a chance to measure their success, or at least measure their aspiration for it, against those already there. Irish students work the bars and restaurants; Latino migrants keep the hedges trim and pools clear of leaves; local students take lifeguard jobs to pluck swimmers from the sea.

But it's also here that the foibles of Manhattan's elite are on vivid display. For many, the competitive intensity of Manhattan is hardly toned down. Women are expected to wear high heels at night; jewellery is worn with swimming costumes (there's a Tiffany in the two-street town of East Hampton). The social glue of fabulousness and gossip propels the season along from opening to charity gala.

Loaves and Fishes, a deli known locally as Thieves and Bitches because it's over-priced and unfriendly, is the hub of gossip. Each summer brings its own narrative (recent chat has been about how much art was damaged in a fire at Larry Gagosian's place – the conclusion was not much, though the fire chief complained that the sculptures on the drive impeded his fire engines).

Set back behind the dune, potato farmers are still digging and pulling spuds, just as they have done since Irish immigrants first settled here in the 17th century. With land at such a premium, it is remarkable that so many have not sold out to developers. Still, each season brings new complaints that the Hamptons are over-run. What they mean, of course, is that they fear being over-run with people that are not our people.

"It's a unique place," says Ed Michaels, chief harbour master with the Marine Patrol of East Hampton Town, whose job it is to protect beaches and waterways. "People came here to get away from other people. But so did everyone else, and that's where the conflict comes in. So they like to complain about everything."

On occasion, the squabbling breaks out into the open. Several years later, even the wealthy Wall Streeters in their substantial beach mansions were aghast at the secretive industrial mogul Ira Rennert who built the largest private house in the US on the beachfront at Wainscott. It's now used as a Jewish study centre that spills groups of black-clad, ultra-orthodox Jews on to local lanes (they never seem to go near the ocean, though). In 2003, Steven Spielberg and other wealthy homeowners around Georgica Pond briefly proposed seceding to establishing their own township called Dune Hampton.

That would not have appealed to Diane McNally, the long-serving clerk of the East Hampton town trustees whose job it is to collect revenue from shellfish permits and judge clamming contests (winners typically come in at just under three pounds). Her job is also to represent and manage common lands for the general public according to the deed of independence granted to East Hampton by James II in 1686 – 90 years before the rest of the country. (The King was not a beach lover – he ceded the area for the price of one sheep per annum.)

McNally hopes a project to boost the stock of winter flounder will be as successful as a previous programme to re-introduce osprey. Today, her mind is on scallop sanctuaries and clams. "A bad clam can cause a lot of problems," she cautions, "and the baymen are tight-lipped about where the good beds are."

But the problem of what to do about people that are not us is a big issue. Beach clubs with restricted memberships, restricted beach access, squads of pimply young cops writing $150 parking tickets, season beach passes that run to hundreds of dollars, a ban on weekend passes to non-residents, are all about one thing: keeping the Hamptons from being over-run.

Locals resist the new homeowners, and everyone resists the aspirant renters who flood the Hamptons in July and August. What protective locals fear, more than anything, is an encroachment of the Jersey Shore experience, of Snooki and her type, with their binge drinking. Even city beaches like Coney Island or Rockaway are considered déclassé with their mountains of flesh, noise and a sea full of fast-food detritus.

Hamptons regulations are often contradictory, run by competing state, village and town ordinances, leaving authorities at a loss to explain their purpose. No horses allowed between May and November; no dogs, leashed or otherwise; no bonfires; no driving; no music; swimming prohibited outside of hours when tanned lifeguards in Baywatch-red swimwear are on duty.

Yet out toward Montauk – the 'East End' – beyond the blonde mothers in their Porsche SUVs, the beach, the sea and people grow wilder. Here, people pay no attention to the social conventions of the Hamptons society and the efforts of wealthy home-owners to control beach access.

"People forget the beach is public property," says lifelong surfer-artist-architect Randy Rosenberg. "You can go down to the beach behind the most expensive house in the Hamptons, lay out a picnic and they can't say a thing." For the past three years on St Patrick's Day, there have been battles between the police and revellers .

The ocean also takes on a different aspect. Several great whites have been sighted this summer off the coast of Cape Cod and Martha's Vineyard, not more than 40 miles away and barely a walk in the park for a large pelagic predator. There hasn't been an attack in Long Island waters since 1916, when four swimmers were taken by a great white, and swimmers are considered more likely to be nipped by schools of aggressive blue fish than by Jaws.

"A vertical fin is a dolphin or a porpoise. If it flops over, it's a shark," explains the 76-year-old lifeguard emeritus JJ 'Big John' Ryan, who has looked after the Long Island beaches for most of his life. Big John instructs young lifeguards, a rite of passage for many young Long Islanders, who perform rescue practice in the surf each morning before the crowds arrive. The lifeguards are a picture-book of the American ideal – young, vigorous, tanned – and Big John considers a beach day like this with clear blues skies and calm, 66-degree water, close to perfection. "I've visited beaches all round the world and believe me, nowhere comes close," he says, before offering a lesson on the correct way to negotiate the surf.

But as it turns out, the competitiveness and squabbling that takes place over the Hamptons beaches ultimately defers to one higher authority: Federal laws that protect the piping plover. The dunes in the Hamptons are one of the only places these tiny shorebirds, barely larger than a sparrow, nest. At least half the estimated 6,500 piping plover population live on the Atlantic coast. They feed at night, darting in and out of the dunes, foraging for insects, marine worms, and crustaceans.

It is for the protection of these nervous birds that the 4 July fireworks are banned on the beach, and it's at least partly why dogs, parties and driving are banned. "People want their own piece of the beach and when they complain, they complain essentially that there are other people on the beach," says harbour-master Jeff Louchheim. But when it comes to the plover, there's nothing any Wall Street billionaire or anyone else can do about it. "There's a lot of life out there," Louchheim considers as he surveys a stretch of coastline before the sun has burned off the morning fog one morning. "But it's the plovers. They're the ones that really control these beaches..."