One of the world's unsung endangered species, the river dolphin, can be saved given sufficient funds and the political will.

Male pink dolphins make nocturnal forays into the small human communities of the Brazilian Amazon, disguised as handsome young men. They seduce women whose husbands are on long fishing trips. How else could so many wives become pregnant?

This sort of myth is prevalent partly because so little is known about the real life of the Amazon river dolphin, or boto, one of four species of river dolphin that occupy some of the world's greatest river systems - the Indus, Ganges, Yangtze, Orinoco and Amazon. River dolphins are very different from their marine counterparts - they have reduced vision or blindness, very flexible bodies and pincer-like jaws armed with formidable teeth. They also share an inability to escape from man. Their habitat is dammed, drained, fished and polluted to an extent far greater than that experienced by other cetaceans (whales, dolphins and porpoises). Small wonder that three river dolphin species are among the five most endangered of all cetaceans, and that the last Yangtze dolphin may die before I do.

To prevent the disappearance of all river dolphins, we must discover why they are in such trouble and remove the causes. A necessary start is to understand their life history and ecology. I began work on the only numerous species, the Amazon dolphin, with Brazilian biologist Vera da Silva in 1991. Rather than use cross-sectional techniques, we use a longitudinal approach. The former involves studying many animals at one moment in their lifetime (actually, at their death). The latter, much more satisfying, requires the following of fewer individuals during a substantial portion of their lifetime. We now know 180 freeze-marked dolphins, some of which are producing their third calves under our watchful gaze.

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Our field base is a raft tethered to trees in the flooded forest. It is surrounded by wildlife I only dreamed about as a kid: dolphins swim beneath you at night, howler monkeys and parrots wake you at dawn. Students maintain dolphin observations year round. Our eyes are supplemented by radio telemetry, allowing tagged animals to be tracked day and night by solar-powered data-loggers situated above the canopy.

We have found no evidence of nocturnal assignations with local women - on the part of dolphins, anyway. But we have learnt what makes this dolphin population tick. The boto's lifestyle is intimately linked to the seasonal flooding of the middle Amazon. This results in huge fish productivity in the inundated forest. In turn, the fish support greater densities of dolphins than are found anywhere else. The boto is a long-lived, slow-reproducing species vulnerable to even modest increases in adult mortality, through entanglement in fishing nets, for example.

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The picture emerging here and in Asia is surprisingly simple, and it explains why most river dolphins are in such dire trouble. These creatures evolved over millions of years to life in pristine tropical rivers with massive water flow and abundant fauna. Disturb the flow with dams, and the whole ecology suffers. Drain the water for irrigation, the wildlife drains with it. Overfish with monofilament nets and line, and dolphins will drown or go hungry. In short, man and riverine wildlife do not mix. The good news is that all but the Chinese dolphin can be rescued in the nick of time, given sufficient resources and political will. But what price a pink dolphin?

Tony Martin is a scientist with the Natural Environment Research Council's Sea Mammal Research Unit at the University of St Andrews.