To be beside the seaside: Simon Calder visits Salton Sea

They call it "the fastest water on earth". As I bobbed effortlessly away from the shore, watching the Santa Rosa mountain range melt in the heat haze, such a superlative seemed implausible.

You know California's shore, of course, featuring the pounding Pacific. Over millennia, the ocean waves have pummelled the coast into an alluring corrugation of beaches and cliffs, and today they toy with surfers and provide a backdrop for dream holidays.

Yet the south-east corner of the Golden State has a secret and strange seashore – 100 miles of rocks and sand and scrub, located in the bleak Colorado Desert close to the Mexican border. It is the perimeter of a vast inland lake that is California's very own Dead Sea, one-third saltier than the Pacific. And that is why bathers become super-bouyant and aquatic speed records can be broken.

"Boaters could set world records easily because of the elevation," Jennie Kelly told me, after I had dried off. The sub-sea-level altitude made engines more powerful, and the extra salinity allowed vessels to ride higher in the water and reduce drag.

Ms Kelly is the director of the Salton Sea History Museum. We talked on the edge of Varner Harbor, a sleepy marina that has seen more masts and better days. It lies towards the north of the Salton Sea – a body of water whose footprint on the map uncannily represents, well, a footprint. The near-perfect imprint off a left foot launching a kick at the Mexican border, indeed. The port is on the left side of the heel.

Unlike the Dead Sea, the Salton Sea does not scroll back far. It didn't even exist at the start of the 20th century, so the historian's task is not exactly Biblical in complexity. The Sea was born – or, given previous incarnations over the centuries, reborn – in 1905. An unusually wet winter in the Colorado River watershed combined with botched exploitation of the waterway for agriculture. The result: the flow of the biggest river in the American South West was diverted from the Gulf of California to a rift astride the San Andreas fault, a desert basin hundreds of feet below the level of the ocean.

By the time the river was back on course, whole communities were inundated, the Southern Pacific Railroad lost its tracks beneath the rising waters, and California had acquired its very own Dead Sea. As with the Holy Land's sunken sea, there is no escape for the water except through evaporation, which explains the high salinity. But unlike the Dead Sea, the Salton Sea is full of life.

The "Pacific Flyway" is the avian equivalent of the Pan-American Highway, stretching from Alaska to the far south of Patagonia. The Salton Sea is one of its main pit stops.

Across a desolate landscape bleached by the sun, I drove my Nissan to the levee. This dyke, more or less located by the little toe, is part of a network that defends the National Wildlife Reserve against any more aquatic misadventures. The reserve is named after the pop star-turned-politician Sonny Bono – a man who had nothing to do with U2 but lots to do with Cher, at one time both his wife and musical partner.

The front half of Sonny & Cher later became mayor of Palm Springs, the nearest oasis to the Salton Sea, and championed its survival against the encroachment of industry and the effluent of agriculture. Mr Bono died in a skiing accident near Lake Tahoe in 1998, but the Salton Sea survives. And judging from the clamour of snow geese feasting by the shore, it remains a crucial filling station for migrating birds. A couple who themselves had migrated a long way from home – home being Guildford – had spent the morning watching waders at the reserve: "Black-necked stilts and American avocets," they reported.

What's for breakfast? Tilapia – hundreds of millions of them. "The tilapia had been imported in order to keep the algae out of the canals," said Jennie. "They made their way down through drainage and into the Sea. They've taken over now. They have no competition."

Success with breeding, breeds disaster – at least for a good few million of the creatures. The high salinity and periodic algae blooms, deplete the oxygen and kill the fish.

Unlike, say, Malibu, a walk along the Salton Sea shore involves picking your way between the ghostly skeletons of tilapia, each looking like the wreckage from a kipper breakfast. More than enough survive to nourish hungry humans. No limits are placed on anglers, and the fish are far tastier than their farmed relatives.

The Salton Sea has bestowed fun as well as food upon the parched south-east of California. In the 1920s, when automobiles were becoming more common but the highways to the Pacific were still poor, the locals could come here to splash and sail. The story is told in the Salton Sea History Museum, which occupies "a very rustic, sort of earthy building," according to Jennie.

The location is right at the back of the heel, between Highway 195 and Whitewater Cove (don't be misled by the name: kayakers are rarely disturbed by more than a ripple). The current exhibition features the Rancho Dos Palmas, a resort founded in 1937 by Gertrude Voss Tenderich – who made her fortune starting up the Tampax Corporation. The museum shop sells souvenir ashtrays first designed in the 1930s that look like someone stepped in the clay.

"I really like the areas that have remnants of our early days," the director told me. "Unfortunately, much of that is under water. At Desert Beach, if you walk to the edge there you can see the foundation of the buildings, of the resort."

The postal address of the museum is Mecca, CA 92254. Unlike the primary shrine of Islam, anyone can visit this municipality regardless of religion. But it's hard to see why anyone other than a Hollywood location scout searching for somewhere to replicate the Dust Bowl would bother. Three-quarters of the pages of the free local paper, the Desert Post, are given over to legal notices foreclosing on properties. Mecca is a tumbleweed town, an unholy crossroads whose only attribute that I could find was Tacos Time on Second Street – much more Mex than Tex.

Yet people still make pilgrimages to the shores of the Salton Sea. "Snowbirds" from the cold northern states migrate south in October or November and stay until spring. They arrive, self-sufficiently, in RVs. To follow them, go to Niland (another place where the good times evaporated long ago), head east away from the Sea along Main Street and over the relaid Southern Pacific tracks, where it becomes Beal Road.

A former US military reserve, with convenient slabs of concrete to serve as hardstanding, has been colonised by sunseekers to such an extent that it is now known as "Slab City". Some in the area are concerned about the trailers and the trash they generate, but a concrete former sentry box has been daubed with the slogan "The Last Free Place".

To free the spirit, nudge the Nissan towards Salvation Mountain. Leonard Knight may have mis-spent the first half of his life in the indulgent manner of many Californian baby-boomers, but he has devoted the latter half to recycling of a Biblical kind – creating a Holy Land close to the state's Dead Sea.

"God never fails," is how he introduces Salvation Mountain. The Almighty, abetted by Mr Knight plus lots of mud, straw and industrial quantities of emulsion paint, has created a hillock daubed with slogans for the spirit taken from scripture.

Every surface of the adobe upland is decorated, parts in deck-chair stripes, interspersed with mirage-like tranches of cool pine forests. At the skirts of this shrine a scattering of rusting old vehicles supplicate like sinners, their tyres deflated but their panels uplifted by the revelation that "God is Love".

Climb to the top for a view, from Salvation Mountain, of the Chocolate Mountains (a real range, made of real rock, to the north-east). To the south-west, that haze is the sun searing the Salton Sea, intensifying the tang of salinity.

Like every self-respecting body of water, the Salton Sea has its own Facebook page – introduced by a quote from one long-time local: "All the normal people have left or died." Perhaps they will start to return, if plans to stabilise or reduce the salt content are realised. And, if normal tourists start to return, the region will be resuscitated.

"We have the natural history, with all the wildlife, we have the intriguing history of the sea and its formation, we have a fascinating history," said Jennie Kelly. "It seems like the European visitors have a greater appreciation for the history of places than sometimes our American folks do. But my job is to create that wonder of our history in everybody."

Time to tiptoe through the tilapia and make a bigger splash.

Travel essentials: Salton Sea

Getting there

* The easiest access for British visitors is via San Diego, served non-stop from Heathrow by British Airways. The writer paid £552 return; significantly lower fares are available for one-stop flights, for example on Delta from Gatwick via Atlanta and on US Airways from Manchester via Philadelphia.

Staying there

* The Oasis Mobile Home and RV Park in Niland (001 760 359 0411) may have some rooms available. Alternatively, there is plenty of choice in Palm Springs and Twentynine Palms, where the lodging of choice is the Harmony Motel (001 760 367 3351; harmonymotel.com) – where U2 (but not Sonny Bono) stayed.

Seeing there

* Salton Sea History Museum, 72-120 S. Lincoln Street, Mecca (001 760 574 5471; saltonseamuseum.org). Open 10am-4pm from Friday to Tuesday.

* Salton on screen: The Salton Sea is the subject of Simon Calder's latest travel video. See it at independent.co.uk/salton.

More information

* California State Parks (001 916 653 6995; parks.ca.gov).