Some people in the Bay of Plenty are upset small vessels as well as fishing and diving will be allowed in the waters around the Astrolabe Reef as of 8am Tuesday.
They say the exclusion zone has allowed marine life to thrive, but now all that will be undone.
The regional harbour master is making changes to the exclusion zone in the area off the coast of Tauranga, which has been in place since container ship Rena foundered on the reef in October 2011.
With salvage work finished in the area, the reef is being reopened to vessels under 500 tonnes.
Save Astrolabe Reef campaign leader, Te Atarangi Sayers, who is also a marine biologist, said it was incredibly disappointing news.
"Essentially we're going to go back to pre-Rena conditions within a matter of months, there's no if, buts, or maybes about it.
"I mean, the last five years of biological bounce-back that we've seen at Astrolabe and Otaiti will be completely gone in the next three to four months," Mr Sayers said.
Maritime New Zealand has withdrawn two statutory notices that had declared the wreck hazardous to navigation.
Bay of Plenty regional harbour master Peter Buel said he could not exclude people from an area where there was no maritime safety risk.
"Ever since the incident, there's been work going on the reef, salvage work, so as long as that work [was] ongoing, for the safety of the people doing the job, we kept an exclusion zone over the entire area.
"The work is finishing today so the exclusion zone will be amended, commencing as of tomorrow (Tuesday.)"
Forest and Bird central North Island regional manager Alan Fleming said Minister for Primary Industries Nathan Guy needed to urgently intervene and extend the exclusion zone for another two years, to allow for a discussion around how to best protect the reef's biodiversity.
"I'd just ask that the minister consider the wide support for maintaining the exclusion zone so that the community can have the conversation about its future protection."
Forest and Bird supports a bid by Save Astrolabe Reef to get the Ministry for Primary Industries to have the exclusion zone temporarily extended to allow for fishing stock to continue to replenish.
But Mr Sayers said the community was not being heard, and he was worried the government's next move might be too little, too late.
"Potentially the minister could say tomorrow [close the area around the reef] but the issue is that, is there really a willingness?"
The Ministry for Primary Industries said it was considering the request to extend the exclusion zone, and keep boats away from the reef.