KAMPALA - Defying crocodiles and hippos, a group of rafters has completed the final leg of a journey down the world's longest river, reopening 150 years of debate over the true source of the Nile.

Last year the team traversed its rapids from Jinja, on the Ugandan shores of Lake Victoria, for 4-1/2 months to Egypt's Mediterranean coast - an epic feat many considered the first full descent of the mighty river.

But others insist the true source of the White Nile is little more than a muddy puddle deep in the Rwandan mountains, which feeds the Kagera River flowing east into the lake, then across it to Jinja.

"After we completed the first expedition in May 2004, there were definitely a few non-believers who said we had not started from the real source," team leader Hendri Coetzee said.

Early last month, the group set out again to confound their critics and raft the Kagera down to Lake Victoria. That journey had not been attempted for more than 100 years, and added 750 km to the 6,700 km they did last year.

"This has consumed the last two years of my life, and it's great to have finally finished and to have put it beyond doubt," Coetzee told Reuters by telephone after pulling his boat out of the river at Jinja late on Saturday.

The team began by hacking through dense jungle for two days, tracing the Kagera from its first dirty pool until it became swollen enough to launch their 4.2-metre inflatable raft.

Once on the river, they had to stay alert for hippos, crocodiles and treacherous, uncharted whitewater rapids.

Members of the group - which included four South Africans, a Ugandan, a Canadian, a Belgian and a Briton - scouted ahead in kayaks to assess the approaching dangers.

"Two or three times we had to get out and carry everything round some pretty serious waterfalls," said 28-year-old Briton Tristan McCommell. "There was a lot of sleeping in swamps."

Debate over the real source of the White Nile has raged since the late 1850s, when British explorers like John Hanning Speke, Richard Burton and Samuel Baker began staking their reputations, fortunes and health on finding it.

It was not until the 1874 expedition by American journalist Henry Stanley - when he found missing British missionary David Livingstone and circumnavigated Lake Victoria and Lake Tanganyika for the first time - that much of the area was mapped and many questions answered.

While there is just a perceptible drift of water from the Kagera mouth across Lake Victoria to Jinja, most geographers place the source of the river at the Ugandan outlet from the giant lake.