Anne Webber says she understands council needs to sell surplus land - just not Cornmarket Reserve.
The Whanganui woman is behind a petition against the proposed sale of part of the reserve near Dublin St Bridge and said it needed to stay as vacant green space.
"I think it's a gateway to Whanganui coming from the north," Mrs Webber said.
"It's a nice space and doesn't need a building on it, absolutely not. I think it balances out Kowhai Park a bit.
"It's just a nice space and it's part of the river. It actually enhances the river."
Cornmarket Reserve is one of 23 properties Wanganui District Council has identified as surplus.
The council's draft property portfolio investment plan proposes selling them to pay off debt and invest.
Mrs Webber said she understood that.
"I do think in this day and age council do have to look at what they own and what they need."
But she had met no one who supported selling the reserve, and her petition which is available to sign at Yellow House Cafe across the road has collected about 300 signatures.
"I would hate to see it sold and everyone I've spoken to has the exact same opinion. No one has said it should be sold."
Mrs Webber said she started the petition to make people aware that it was on a list of potential sites for sale.
"I thought if I don't say something I'll be regretting it if it got sold."
Councillors voting last year to put the plan out for public consultation expected some sites to be controversial.
"Some of these properties no one will care about. One or two properties everyone will care about," Whanganui mayor Hamish McDouall said.
Public consultation of the proposed plan is open until February 16 and people can have a further say during the council's long term plan consultation in 2018.
For more information visit www.whanganui.govt.nz.