Can you really trust your guidebook?

It would be hard to make it sound more inviting. Lake Challa, in Kenya's Tsavo West National Park, "is a deep and unbelievably transparent blue", according to the Rough Guide to Kenya.

"It once had a population of harmless dwarf crocodiles, but these have died out and it's inhabited today only by mythical monsters and paddled over by a few fishermen in dugouts ... The lake itself is bilharzia-free, which makes for a very pleasant swim."

Last Friday, however, one of the mythical monsters of Lake Challa grabbed an 18-year-old British girl, Amy Nicholls. Two days later, Kenyan navy divers found her body. She was said to have suffered terrible wounds; her right arm was missing. According to Nicholls's friend Elspeth Harley, Nicholls's last words were: "It's got my feet, it's a crocodile." Clearly, Lake Challa is no longer the spot for a pleasant swim.

While the Nicholls family struggles with its grief, other travellers will be asking themselves whether guidebooks themselves - now considered an essential part of any wanderer's luggage - are to be trusted.

Although Nicholls - a volunteer working on a nearby environmental project - was also said to have consulted locals before entering the water, the misinformation in the guidebook bears clear responsibility. As Jane Durham, managing director of Okavango Tours and Safaris, which sends tours to the area, put it: "It is one hell of a slip-up."

Rough Guides' Claire Southern yesterday explained that the guide was "being updated. Obviously there will be a lot of change to the editorial. But guides are not foolproof."

Yet they are relied upon by many, a state of affairs that deserves now to be challenged. As Kerry Glen, a tour operator at Okavango, puts it: "I grew up in Kenya and swam in Lake Challa as a teenager. My father says my mother was crazy to let us. There have always been crocodiles there. And they're known to have eaten people." According to Glen, Nicholls's own local enquiries may have been confused. "Apparently there was a misunderstanding. The person she asked thought she was referring to a nearby swimming pool, not the lake."

The episode is, however, part of a bigger trend, says the independent guidebook writer and publisher Hilary Bradt. "Tourists these days are so afraid of the dangers of being mugged or attacked that it's almost gone the wrong way. And guidebooks have also gone overboard warning people about these dangers. In the process they have underplayed the danger of animals."

Bradt - whose 1977 Backpacker's Guide was the first internationally available guidebook to Africa - says there is a woeful level of ignorance about dangerous animals. "I have just returned from one of those posh lodges in Botswana. There was a couple staying there who had to be restrained from jumping out of their boat to photograph a hippo with her calf. If they'd done so they probably wouldn't be alive today." Animals, she says, are "unpredictable".

But correctly identifying risk spots is difficult for any guidebook writer, she points out. The 1999 edition of her guide to Madagascar claims at one point that a particular lake contains "crocodiles [that] are friendly and don't bother swimmers". Last year, two local guides were eaten by crocodiles in the same lake, and she is now duly updating her guide. While aware that her defence "would not stand up in court", she explains that her source was no ordinary reader's comment. "It came from a man who'd worked in the area for years for a charity. He had always swum perfectly safely in the lake."

The problem with guidebooks, points out Miranda Haines, executive editor of Geographical magazine, is that "by the time they get to the bookshop they're already out of date". And yet at their best they can be even more reliable than locals, insists Bradt. "Often a guidebook will give you far better information than the people will. In Madagascar, for example, there are no venomous snakes and yet people will often warn you about poisonous snakes. The superstitions of the local people often overlay reality."

And no one, says Shane Winser, who runs the Royal Geographical Society's Expedition Advisory Service, would wish a return to the days before guidebooks. "When I started working here in the 1970s there were hardly any guidebooks available and so the exchange of information was very low.

"Guidebooks are very good at raising all sorts of issues, particularly issues of safety and they make people aware of the risks of travelling. We are much better off with them than without them. I'd also hate it if this episode made guidebooks more cautious - we need their opinions."

Yet Winser, a highly experienced traveller herself, admits that the killing could have repercussions for her own summer plans. "I'm taking my children to Kenya later this year. What am I going to do? Because of this particular death I might well be more reluctant to let them go swimming." Though this is, she admits, a largely emotional reaction. "It's more likely my son will be killed behind the wheel of a car when he's in Kenya. That's a real risk."

In its defence, Rough Guides claims that the information about Lake Challa came - in common with all the details in its guides - from a number of sources and was judged to be reliable. Winser is supportive, adding that this is "not an issue of blame. But in Africa the risk from dangerous animals is always there. When you gamble with a crocodile, it is a big gamble. Next time you want to take a photo of an elephant, or get close to a bear, remember that these are very dangerous animals. Treat them with respect."

? Edward Marriott is the author of The Lost Tribe and Wild Shore: Life and Death with Nicaragua's Last Shark Hunters (both published by Picador).