Mr Chapman had wanted to speak to councillors at Wednesday's Environment Committee meeting but was declined but was able to address councillors via email.
But Ruapehu's incumbent regional councillor Bruce Rollinson said that was a "sledgehammer" approach.
Mr Rollinson said when the One Plan was drawn up it was deemed the level of farming in the catchment was sustainable.
Making it a priority catchment would require a plan change, he said.
"To get a plan change, that's essentially and whole new re-litigation of the One Plan."
Mr Rollinson said instead the catchment should be focused on in terms of monitoring it more closely and increasing environmental grants to the area.
"(Farmers) don't react well to regulation, they react well to community initiatives."