The WCO would preserve the rivers in their current state, which meant existing water rights would continue, he said.
"This extraordinary set of claims that are being made, that 97 per cent of water rights will be cancelled, thousands of jobs lost, community destroyed, this is complete garbage," he said.
"People are being cynically manipulated into this sort of catastrophic thinking."
The campaign has used voices from the region's businesses, politicians, and primary sector - including horticulture, agriculture and viticulture groups.
Hastings-based PR company ATTN! Marketing has also been enlisted to work on the campaign. Aside from producing media statements, the extent of their involvement is not known.
A point of contention he had with the company, Mr Hague said, was that they did not appear to be a member of the national body - Public Relations Institute New Zealand - so were not bound by its code of ethics.
"That means they are not subject to the ethical requirements to name their client and that any claims made would need to be well founded, which would be the case for a normal part of the PR industry.
"Many of the claims that have been made, and certainly the claims that have got people so upset and disturbed, are not well founded at all.
"There is no prospect that people will lose their jobs or that water rights will be cancelled or that the community will be destroyed, that's just not going to happen, that isn't what a WCO does."
Mr Hague had received no reply to his questions about ATTN's clients, their exact involvement in the campaign, and whether they adhered to a code of ethics.
When the same questions were put to them by Hawke's Bay Today, ATTN! Marketing director Catherine Wedd said it represented a "diverse range" of Hawke's Bay businesses who believed the community needed to be informed "about the impact that a water conservation order will have on everyone".
"The community has the right to speak out against the WCO and make an informed decision. The communication about the Water Conservation Order is well informed and appropriate. The WCO rally is an opportunity for the community to stand up for Hawke's Bay and what they believe in," she said.
"The opinion pieces which have been published in the Hawke's Bay Today are the opinions of the authors who have written them. Attn Marketing PR has not written any of these.
"Attn Marketing PR is an influencing and reputation-building marketing and communications company. As PR experts we ensure we are well informed and always adhere to strong ethical values."
Mr Hague visited Hawke's Bay last week, and said he was concerned about the "vilification" that had been directed toward local members.
"It's a shame that a campaign has been mounted that has portrayed the application in such a pejorative and misleading way, which has tended to polarise the community.
"I just hadn't anticipated this level of misinformation."
One of the main arguments against the WCO is a preference for the community-led water management TANK process - which at the time of the application was "pretty dysfunctional" Mr Hague said.
"I get the [Hawke's Bay Regional Council's] idea that TANK should be allowed to continue and finish its work, and that is the reason that the applicant groups have suggested timetabling that would allow that to occur before the special tribunal gets to the point of considering any rules for the lower part of the river.
"I think that's a pretty good accommodation of the issues around TANK."
Forest and Bird is one of six applicants of the WCO. Last week it lodged a memorandum sharing concerns with the special tribunal hearing the application.
These were addressed at Friday's pre-hearing conference, with tribunal chairman Richard Fowler saying there was no prospect of the tribunal being influenced by public statements, or rallies.
"Anybody who thinks that doing those things - that is either publicly demonstrating or making statements to the media - will have the slightest effect on us, frankly that's just laughable, it's just a complete waste of time."