Immediate action is needed to stop people from driving vehicles near the mouth of the Waikanae River area, north of Wellington, a concerned resident believes.
Dr John Robinson, from Waikanae, has written to Minister of Conservation Eugenie Sage, saying the sandspit was a national treasure environmentally and recreationally but vehicles were often driven and parked in the area when they weren't allowed.
"These are most numerous, and do the most damage to the ecosystem, during the whitebaiting season," he wrote.
Dr Robinson said he was advised by the Department of Conservation that vehicles were breaching bylaws by travelling along the beach into the Waikanae Estuary Scientific Reserve, which in turn "can damage shellfish beds, endanger wildlife such as nesting birds and, of course, people".
And while the local council issues permits for people wanting to drive on the beach for whitebaiting, it was "absurd since the whitebaiting takes place along the river in the scientific reserve, which is excluded in the permits".
"The practical result is that many vehicles do drive there, never mind what words are written on the paper."
Mr Robinson said Kapiti Coast District Council was "sympathetic but has not told of any action they might be taking" and an iwi group "did not tell me of any policy but claimed special rights dating from 1840".
"The situation is sad and ongoing.
"Without action 2018 will see the same trashing of the environment that I saw in 2017, which has gone on for years," he said.
"My inquiries have told me that no action is under way or planned."
He said, "Something must be done right now.
"The Department of Conservation should insist on protection of the scientific reserve.
"The Kapiti Coast District Council should stop issuing permits to drive on the beach for whitebaiting.
"The law should then be upheld, actively policed and obeyed by all."
He invited Sage and all others "with some responsibility for this environmental gem" to "meet with me and to set out a plan for immediate action".