The Department of Conservation and the conservation minister are refusing to explain why it changed its mind within 48 hours about making a submission pushing for more scrutiny of the water quality impacts of a big dam project.

A page from a just-released DoC report shows the department told Minister Nick Smith on Monday 29 July that its preliminary view was that it should lodge a submission asking for an independent review on how the Ruataniwha Dam might harm the Tukituki River in Hawke's Bay.

A DoC email that evening said the Minister was concerned and wanted to see the submission.

By the Wednesday of that week, and with the submission due by Friday, it had changed so that it said nothing about water quality and the Tukituki River and instead consisted of a few lines about the dam.

Dr Smith has said he was aware of normal internal debate within the department about whether or not its submission to the Environmental Protection Agency should raise concerns about water quality.

Dr Smith has denied in Parliament knowing anything about a long draft which DoC had prepared in the run up to presenting its preliminary view to him on 29 July.

The Green Party says the document released by the Minister of Conservation's office shows Dr Smith is playing fast and loose with the facts on the Ruataniwha Dam proposal.

Green Party Co-Leader Russel Norman says the document blows holes in Dr Smith's story that he didn't know the submission existed until this week.

He says within 48 hours of Dr Smith meeting with officials the 32 page submission had been reduced to 2 paragraphs which didn't even mention water quality.

Dr Smith's office says he has nothing further to add.