Tasman's mayor says a review into the over-budget Waimea Dam, southeast of Nelson, should not start until the project's completed.
Initially estimated to cost $76 million, the price tag rose to $105m when the council approved the project in 2018.
Now under construction, Waimea Water is forecasting it to cost $158m.
The multimillion-dollar dam was first proposed in 2003 and its construction started in 2019, after years of rising controversy over its merits.
On Thursday, protesters called for an inquiry into the rising bill, but mayor Tim King said it is too late to halt the project.
"My personal view is probably if there's going to be a review into the project, the time to do that is once it's complete and where it ended up and you can look at the whole process not part of it.
"I guess it remains to be seen what the council's decision is and [if] they want to do a review and if they do when."
He said independently reviewing the project after completion, will provide a better understanding of what has gone wrong.
"We're committed to building the dam, there's really no opportunity to stop building it halfway through and so the challenge is working out how to get it completed, who's going to pay for it and who's going to pay the cost of completion."
The most recent cost increases have been blamed on Covid-related costs and associated delays.
When finished, the Waimea Dam will be 53 metres high and hold 13 billion litres of water - that's more than the contents of 5000 Olympic swimming pools.