The Government is close to a deal to return New Zealand's longest river to Maori claimants.

The deal is likely to be announced at celebrations marking the 40th anniversary of the coronation of Dame Te Atairangikaahu as Maori Queen. The festivities begin on Wednesday.

"The river is our ancestor, and we want our tupuna awa [river ancestor] returned," said a senior Tainui source who would not be named.

The Waikato River claim was part of the Wai 30 claim lodged by the late Sir Robert Mahuta, father of Tainui MP Nanaia Mahuta and brother of Dame Te Ata.

It is understood staff and senior Tainui leaders, including chairman Tuku Morgan and co-negotiator Lady Raiha Mahuta, have been involved in talks with Treaty Minister Mark Burton and Office of Treaty Settlements officials most of this week.

The tribe will expect at the least a co-management role in the river, a major economic resource in the region and the source of some of Auckland's drinking water.

It is understood that although few hard details have been agreed between the two groups, there is a confidence that an agreement in principle will be ready by Monday week when Prime Minister Helen Clark attends the celebrations.

The claim includes the banks of the river, its tributaries and associated flood plains and west coast harbours. The claim was set aside from the tribe's 1995 $170 million land settlement.

The dollar value of the settlement is also not known, but a 2004 settlement for the return of 13 of Rotorua's 14 lakes included a $10 million package for Te Arawa.

The settlement is also likely to set a precedent for long-standing claims against the Crown from the Whanganui iwi over the Whanganui River, and Taupo-based Tuwharetoa.

Tribal and political sources said the Government had ratcheted up enthusiasm to make a deal with the tribe after years of little progress. They said pressure from Helen Clark had resulted in the increased activity.

Event organisers are understood to have already scheduled the Prime Minister's visit and the planned announcement.

The anniversary celebrations will be one of the largest events on the Maori calendar.

More than 25,000 people are expected to attend, including leaders and dignitaries from throughout the country and the Pacific.

The National Party's Maori affairs spokesman, Gerry Brownlee, said the Government's enthusiasm was self-serving and driven by a desire to reward Tainui and curry favour with Maori.

"These negotiations have been going on for many, many years. By and large the Governments have held a line which reflects the intent of the Foreshore and Seabed Act.

"The Government are about to give that away to curry favour with Maori and effectively buy votes at what is a very important Maori occasion."

Mr Brownlee also accused the Government of using negotiations to reward Nanaia Mahuta for changing her stance on the foreshore legislation.

Ms Mahuta, now a Cabinet minister, retained her Tainui seat after fending off a strong campaign by Maori Party candidate Angeline Greensill in last year's general election.

"This arrangement is perhaps also an endorsement of the Maori Queen and her support for the Labour Party's ascendancy in Tainui over the Maori Party at the last election."

Mr Brownlee said there were many groups who should be consulted regarding the future of the river before a deal was struck.

"I think the process should see everyone who has an interest in Auckland water having a say."

Tainui chairman Mr Morgan did not return calls yesterday.