All eight councillors defiantly told Hawke's Bay Today yesterday they were not the source of the leak.
Councillor Terry Kingston, however, said Mr Butler's comments might damage the future of the dam project.
"The comments [slimeball councillor] are in my opinion certainly not helpful in getting the go-ahead for the Ruataniwha dam ... The future of the dam is essential for the economic and employment growth of Central Hawke's Bay.
"I'm not aware of which councillor leaked it. We [councillors] all have our strengths and weaknesses but being a slimeball is certainly not one of them."
He believed Mr Butler's name calling, and the comments about Mr Tomoana, were "offensive" and achieved nothing but a poor reflection on a council wanting to grow and support Central Hawke's Bay.
Councillor Andrew Watts said Mr Butler and the councillors were meeting tomorrow, when the issue would be discussed.
Councillor Kelly Annand was reluctant to comment further on Mr Butler's comments before the matter had been discussed by the councillors and mayor.
Councillor Sally Butler, who is also Mr Butler's sister-in-law, said the leak was a breach of trust.
"He obviously felt it was a breach of trust and any communications like that are private. I would assume he thought that if anyone had a problem they should come to him directly."
Councillor Mark Williams said he had "no idea" who might be the source of the leak but said it was not a good look for council.
"I think if I was in the same shoes as Peter [Butler] I would have done the same thing," referring to the slimeball comment, he said.
Councillor Maitland Manning said Mr Butler's reaction was unfortunate but felt he had been let down by the councillor who leaked the newsletter.
"If someone has a problem they should front up in person and sort it out."
Councillor Ian Sharp offered no comment on Mr Butler's description of one of his fellow colleagues.
Councillor Terry Story said Mr Butler's comments may have been said in the "heat of the moment" but decided against commenting further.
Mr Tomoana has expressed disappointment at the comment and maintained that the iwi supported activities on the Tukituki River and its stance against the dam was aimed at protecting the waterways.