Speke thought he had solved one of the greatest mysteries of 19th-century geography. What he didn't know was that for the Nile to be the longest river in the world, the longest tributary leading into Lake Victoria from the south had to be added to its length.
Others have traveled the length of the river from Lake Victoria to the Mediterranean Sea. But Ascend the Nile is the first expedition believed to have traveled the Nile from its mouth to its ultimate source.
"Our primary objective was to travel the length of the Nile to its longest source and measure it [electronically] for the first time from the water," said McLeay.
Traveling in small inflatable powerboats known as Zap Cats and armed with global positioning system (GPS) technology, the team began its journey from Egypt on September 21 last year.
The first stage of the trek, through Egypt and northern Sudan, proved to be a breeze.
Then the explorers encountered the Sudd. A papyrus reed-covered swamp the size of France, the Sudd historically has separated Arab and Muslim northern Sudan from the black and mainly Christian southern region.
Few people venture into the stifling, humid Sudd. The explorers soon discovered why.
Around the clock, hordes of malaria-carrying mosquitoes, skinny enough to penetrate mosquito nets, mercilessly attacked the travelers. During the day, tsetse and razor flies assaulted them whenever they stopped.
"I felt like some sort of bait at the mercy of inhabitants of this vast swamp," McLeay said.
To navigate the Sudd's myriad channels, some of which go on for 60 miles only to come to a dead end, the team members downloaded Google Earth maps to their laptops.
But their primary form of navigation turned out to be the pesky water hyacinth, a floating water plant that was introduced into the Nile basin in the late 1800s and invaded Lake Victoria in the 1980s. The plant floats the length of the Nile all the way from Lake Victoria.
"Where the river forked, we always followed the channel with the water hyacinth in it," McLeay said.
Farther south, crocodiles and hippos began to clog the river.
In the Murchison Falls National Park in Uganda, the team experienced three crocodile attacks. One beast invaded the camp where the team was settled for the night. Another time, McLeay had to run over a large crocodile with his boat after it charged the travelers.
The biggest threat, however, turned out not to be animals but people.
Uganda has come a long way from the dark days of Idi Amin in the 1970s. Today it has a growing economy and improved security. But the northern part is still plagued by armed attacks from a variety of hostile groups, particularly against civilians. Tourists are advised not to visit Murchison Falls because of possible rebel attacks.
In early November last year, the team encountered some problems with its equipment. Facing an impassable set of rapids in the middle of the park, McLeay, who lives in Uganda, requested help from a friend, Steve Willis, a former British diplomat who ran a backpackers camp, to drive the team around the rapids.
During that drive, the team suddenly came under fire from rebels.
"I was seated in the passenger seat and looked ahead of us on the road to find myself staring down the muzzle of an automatic weapon which was releasing rounds into our vehicle," McLeay said.
One rear tire was shot out as Willis drove the vehicle off the road. The passengers, knowing they had to get out of the vehicle to survive, jumped out. McLeay ran for miles, moving swiftly through the tall thick grass until he knew he was not being pursued.
McGrigor, however, had broken his leg and was unable to run. The rebels found him quickly and forced him to return to the vehicle and help them loot it before they set it on fire and fled. They left McGrigor behind, alive.
Willis, who was married with a two-year-old son, was killed in the initial attack.
In early March of this year the team got back on the Nile and continued south. Passing through Lake Victoria and Tanzania, the explorers headed into Rwanda.
There, the thick Nyungwe forest turned out to be almost impenetrable in places.
"We did our best to follow our Pygmy guide but there were no trails and none of our guides had ever been there before," McLeay said. "We had to rely heavily on our GPS's to guide us through this incredible area."
On March 31 they finally arrived at what McGrigor calls a "muddy hole" in the dense forest, the site determined by the team to be the longest source of the Nile.
"We know we are correct because we have studied the maps in detail and have now physically traced the longest source on the ground," said McLeay. "We've measured the river electronically using GPS tracks and now have the electronic data to prove the Nile is 6,719 kilometers [4,175 miles] in length."
The expedition, while an astonishing feat, may not completely settle the debate about the river's length.
"The concept of a river's source is not a clearly defined one and is open to a number of interpretations," said Juan Jose Valdes, a National Geographic Society senior cartographer. "In the case of the Nile, as with the Amazon, the enormity and complexity of the river system makes the use of the term 'source' a troublesome issue."
The National Geographic Society has traditionally recognized two sources of the Nile, one in Rwanda and one in Burundi, farther south. But Valdes admits that the Society's coordinates were obtained from cartographic sources before the advent of the GPS.
"In the case of the Ascend of the Nile expedition, their coordinates are a bit more exact than ours," he said.
McLeay says the experience of the Nile awed him.
"It flows through areas that time has passed by," he said. "Even in today's world of spacecraft, instant communication, and satellite imagery, much of the Nile remains clouded in mystery. No other river in the world commands as much respect from mankind."
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