'She doesn't like swimmers!" cried a man on the shore as Eric Block lifted his vulnerably Speedo-clad body from the water.
He was referring to Lulu the goose, who flapped and squawked anxiously at the foreign bodies gliding past, her hostile beak ominously close to Block's toes. But fair enough. We were in her territory - a bucolic stretch of river running east from Radcot Bridge, an 800-year-old stone arch said to be the oldest on the Thames.
Yes, that Thames. Despite comments from friends like "Do you need shots for that?" our gang of a dozen swimmers - ranging from amateur triathletes to hardy teachers like Block - had all signed up for a 14-kilometre, two-day crawl hosted by SwimTrek in pretty much the last place you'd expect to find even the keenest water babies.
Then again, SwimTrek's clientele are the types who believe it's much more satisfying to view land from the water than the other way around. Not only do they bathe year-round in the local lido - the English term for an unsheltered (and unheated) swimming pool - they talk about doing 10-kilometre swims as routine and of peers who swim the English Channel - both ways.
But if a decade ago that kind of swim was a feat worthy of newspaper coverage, these days it's about as extraordinary as running a marathon. There are regular open-water swims everywhere from Australia to Ontario, ranging from five to 18 kilometres.
And for avid crawlers who find they are spending more of their vacation fraternizing with the creatures offshore than with their families on it, a handful of swim-tour operators are offering packages that combine challenging - but not over-the-top - swims with the opportunity to enjoy the pleasures of dry land.
Swim Art, for example, a San Francisco-based company, not only guides swimmers on one-day swims to Alcatraz and the Golden Gate Bridge, they offer a weekend outing to Lake Tahoe, where participants tackle three lakes - including a full-moon swim in Meeks Bay.
Come winter the focus shifts south, where Ocean Ducks takes swimmers to the coast of Chile for power crawls of three to 12 kilometres. Some swims run just off quiet beaches 90 minutes from Santiago. Others guide groups past rugged, rocky shores where waves can rise 10 to 15 feet.
Then there's SwimVacation. The mission of its founder, a former Division 1 collegiate swimmer who goes by the nickname Hopper, is to spread the gospel of an active, "completely aquatic experience" to the sort of customer who prefers to watch the action from the beach. "It's one of my ongoing challenges," he says.
As it stands, Hopper has attracted his share of competitive swimmers and triathletes, who regard winter training as an unnecessary evil. Far better, they reckon, to book a room aboard the Promenade, SwimVacation's 65-foot sailing yacht in the British Virgin Islands. It's equipped with five guest cabins and staff who serve sundowners from the open bar.
"It's a high-end, all-inclusive vacation," says Hopper. "Warm towels after swims, gourmet meals, fine wines and fancy Caribbean cocktails."
Back on the Thames, however, we camp. Sure, SwimTrek leads swimming safaris in more luxurious conditions. In fact, the company launched in 2003 with an island-hopping adventure in Greece, added a tour through the coastal islands of Croatia a year later and, five years on, guides groups around Gozo in Malta, Finland and Bavaria. But on our tour of the river that most Brits think of as a vast, murky graveyard of detritus, we end our swim by drying off and pitching our tents.
