From the Telegraph.UK:
By Michael Howie, La Paz
But for the anacondas that live in the swamps surrounding the Yacuma River in northern Bolivia, this invasion of gap year travellers and other hardy tourists is proving disastrous.
Biologists say the entire population of anacondas in one of the jewels of the Amazon basin will be wiped out within three years because of the deadly effect on the snakes of the insect repellant used by most backpackers to help protect against malaria.
The number of tourists going on tours of the pampas that snake there way through jungle and grasslands 250 miles north of La Paz has exploded from a few hundred to nearly 12,000 a year in the past decade.
Travellers are enticed by the promise of getting up close and personal with the world's largest snake - sometimes picking them up and hlding them - as well as swimming with river dolphins, catching pirhanas, and spotting monkeys, sloths and an array of other flora and fauna.
But sightings of the snake are becoming increasingly elusive and as many as 30 of the awe-inspiring creatures, which can measure up to 30ft in length and are known to strangle and devour prey as diverse as caiman crocodiles and cows, are being found dead every year, according to local guides.
Roberto Justiniano, a tour guide and biologist working closely with other scientists to assess the impact of the unrestrained tourism boom, revealed that the growing quantity of toxins being washed into the waterways from travellers is proving too much for the anacondas.
"The high-strength insect repellant that tourists use to protect themselves from mosquitos is absolutely fatal to the anacondas.
"They are amphibians and breath through their skin. The insect repellant, along with some types of sun cream, is extremely toxic. It is getting washed into the pampas and left in the swamps where tourists are hunting for the snakes.
"We are finding between 25 and 30 dead anacondas which have been poisoned. It is terrible."
Amphibians, such as snakes and frogs, are highly susceptible to the chemicals contained in many types of insect repellant, in particular those that contain DEET. This is partly because they breathe and absorb water through their skin, providing an easier way for contaminants to enter the animal's body. Environmentalists recommend using safer insect repellants based on natural oils, but many tourists complains these are less effective.
Zoologists estimate that only around 200 anacondas remain in the Yacuma River swamps, a sharp fall from the population of nearly 1,000 a few years ago.
"A few years years ago you had a 90 per cent chance of seeing anacondas - maybe three or four together. Now you are very lucky if you see one."
He added: "A study has been carried out by other biologists which shows the ecosystem will collapse in three years if things continue as they are."
The fear is that insects, fish and smaller amphibians would be wiped out within the river basin, resulting in the collapse of the entire food chain.