Four East African states, including Tanzania, have signed an agreement to seek more water from the River Nile – a move strongly opposed by Egypt and Sudan.
Under colonial-era accords, the two countries get a staggering 90 percent of the river's water.
Upstream countries including Tanzania, Uganda, Rwanda and Ethiopia say it is unfair and want a new deal but nothing has been agreed in 13 years of talks.
A further three countries were represented at the meeting in Entebbe last week, Uganda, and may sign up later.
Analysts say there is a danger that the split could hamper any further efforts for all nine countries involved to negotiate how the waters should be shared.
"If we don't have an agreed co-operative framework, there will be no peace," Kenya's director of water resources John Nyaro told the BBC before the meeting.
"Where there is no rule of law, the rule of the jungle does not provide peace."
Tanzania, Ethiopia, Uganda, and Rwanda signed the agreement in Entebbe, which would lead to experts determining how much water each country would be entitled to.
Kenya did not sign the agreement as its minister could not attend. Like Burundi and the Democratic Republic of Congo, it sent officials to Entebbe.
Ethiopia, for example - the source of the Blue Nile - contributes an estimated 85 percent of the river waters but is able to make relatively little use of its natural resource.
Rwanda's Environment Minister Stanislas Kamanzi told the BBC: "Egypt has been requesting to defer the signing of the Cooperative Framework Agreement - we couldn't wait any longer, since we have been negotiating for over 10 years."
Egypt and Sudan say they will not sign a new deal unless they are first guaranteed an exact share of the water.
Ahead of the meeting, Ahmed el-Mufti, the legal counsel for Sudan's delegation, told Reuters news agency that all nine countries were close to an agreement, so there was no need for the upstream countries to sign their own deal.
He also said Egypt and Sudan needed water more than those in more fertile regions.
"They have a lot of rain: This is nature," he said. "They do not need the water. Here in Sudan we need water."
Egyptian Foreign Minister Ahmed Abul Gheit has warned that water rights were a "red line" and threatened legal action if a separate deal is reached, the AFP news agency reports.
A colonial-era treaty signed in 1929 between Egypt and Britain gives Egypt majority rights to the Nile's waters. Upstream countries want to be able to use the Nile for development projects like irrigation.