HBRIC chief executive Blair O'Keeffe said he had no further comment to make.
HBRIC's work on the RWSS was criticised by some regional councillors over the past term. The recent local body election saw these councillors become the majority on council.
Yesterday Hawke's Bay Regional council chairman Rex Graham - who has voiced concern on the scheme - thanked Dr Pearce for his contribution while he was in the chair.
When questioned if he asked Dr Pearce to step down, Mr Graham said "no comment".
Wairoa councillor Fenton Wilson, who had served on the HBRIC board with Dr Pearce, spoke highly of what had been achieved with him in the role.
Dr Pearce had done a "colossal" amount of work during his tenure, particularly around Ruataniwha to bring it close to completion, he said.
Although most of the conditions precedent for the scheme were met last term, an independent review of it was commissioned at the inaugural council meeting earlier this month. Councillors also agreed to consult the HBRIC board on issues
which would arise if work on the scheme was suspended.
When asked if he thought these developments were related to Dr Pearce's resignation, Mr Wilson said "I don't think so, but I haven't had those sort of conversations with our new chair".
Mr Wilson added Dr Pearce had a number of other roles, and "this is just a natural progression".
Council chief executive Andrew Newman said Dr Pearce had played a key role in the development process of the RWSS.
"In his time as chairman Andy brought considerable skill and acumen in areas of real relevance including governance, commercial judgement, freshwater hydrology, and management, all of which are very important to the project.
"Andy's fierce intellect and attention to detail meant all people working on the project were challenged to deliver in what remains a demanding and potentially hugely valuable project for Hawke's Bay."
He would not comment on the reasons for Dr Pearce's resignation.
Dr Pearce would remain chairman until December 30.
