Representatives of Auckland's Ngati Whatua hapu say mention of a taniwha under the CBD should not be taken as a threat to a $2.4 billion rail tunnel.

Their advice follows a reminder to transport planners by Auckland Council Maori Statutory Board member Glen Wilcox of a spiritual creature living in an ancient creek now buried under much of Queen St and the Town Hall.

Mr Wilcox caused nervousness at a council committee meeting at the hall on Tuesday when he asked: "What's been done about the taniwha Horotiu who lives just outside here, and that tunnel will be going right through his rohe [territory]?"

His bombshell, which he dropped as a brief mention at the end of a list of general questions about Auckland Mayor Len Brown's top transport project, went unanswered by officials at the meeting.

He has not returned phone calls seeking clarification.

But Ngati Whatua o Orakei cultural adviser Malcolm Paterson said yesterday that the word taniwha meant many things, including a guardian of environmental values.

He believed Mr Wilcox was probably flagging a need for Maori to be consulted properly on the project.

"The analogy I would give you is that this is not too dissimilar to the way people say in English, 'Are you aware of the elephant in the room?'," Mr Paterson said.

"When you hear that in English, people don't think there's literally a large pachyderm in the room.

"Certainly, I wouldn't see that what Glen has said about raising awareness about the stream and what he identifies as a taniwha associated with it would be cause to stop this project."

He believed Ngati Whatua would expect to be engaged fully in such a large project and to influence its design to ensure benefits not just for transport but for the city's environment and heritage.

He said that although the Waihorotiu stream was now out of sight, it still existed, running through pipes and carrying heavy metals to the Waitemata Harbour.

Opportunities should therefore be sought by the project designers "to just not bugger up the ecosystem more, but perhaps enhance it".

Ngati Whatua o Orakei Trust Board chairman Grant Hawke also said he believed Mr Wilcox was simply signalling a need to take care over designing and building the tunnel.

The issue had not yet been brought to his board's attention, he said.

Auckland Transport spokesman Wally Thomas said a detailed route and three station locations for the tunnel - which is likely to skirt around the underground stream and not cross it until it reaches the waterfront - had yet to be finalised.

"There will be extensive engagement and discussion with all parties, including local iwi, once we get the green light to proceed with the [route] designation," he said.

Transport Minister Steven Joyce has said a strong enough business case for the project has yet to be made, although he will not stop the Auckland Council from protecting a route at its expense, which is what Mr Brown intends doing.

Council transport committee chairman Mike Lee would not comment except to say: "Actually, I think there is a taniwha that's blocking the central city rail link and he's not one of your friendly type of taniwha either, and he's called Steven Joyce."

Former Auckland City Council member Graeme Easte, who is now on the Albert-Eden Local Board, gave the Herald a map from the 1840s of the old creek and its tributaries before it was covered over.

A second map of modern Auckland - which he has superimposed on it - shows a western tributary of the stream starting at a spring under the YMCA carpark, to the northeast of Pitt St, between Vincent St and Greys Ave.

Consultants' preferred route would avoid the tributary and the stream, except for drainage through Queen Elizabeth II Square next to Britomart, which was an unreclaimed part of the harbour when the stream was buried.

But Mr Hawke said the taniwha swam into the tide as well as up and down the stream.