Newshub can reveal there are serious doubts about whether camera technology on fishing trawlers would be much use in court as evidence of illegal fishing.
The concerns are raised in a report written by the Ministry for Primary Industries, which the ministry itself is now rubbishing.
Putting cameras on boats was hailed as a way MPI could stop illegal practices and put dodgy skippers before the courts.
The report, which was leaked to Greenpeace, analysed pictures of snapper taken during a trial of cameras on trawl boats operating between Cape Reinga and the East Cape.
It found there are "major challenges" in trying to work out the size of fish seen in the footage because the quality of the video is so poor.
The report says that means if MPI wanted to take an operator to court, they would have limited evidence about the exact size of fish being thrown overboard.
"The Minister is going around telling everyone that these cameras can be used for court action, for compliance and enforcement investigations, and yet MPI's own reports are saying the cameras can't be used for that because they can't accurately determine the length of the fish being dumped," Greenpeace executive director Russel Norman told Newshub.
Knowing the length of fish is important because by law, commercial fishers must keep any snapper over 25 centimetres. Anything below that should be thrown back.
But sometimes legal sized fish that are damaged or discoloured are illegally discarded so operators can catch better quality ones - a practice known as high-grading.
The report says because the video is unclear, if legal sized fish are dumped, MPI will struggle to prove it.
"Which means you can't be prosecuting someone for it. It won't work," Mr Norman said.
However the Minister, Nathan Guy, has rubbished the report, saying it was only "half-finished".
"The scientists had a look at it. They said it's very crappy. They put it in the bin," he told Newshub.
But one of the report's authors, an Associate Professor in Forensic Science who has since left MPI, says he believes the report was suppressed because it highlighted problems.
He rejects the suggestion that it is was poor quality or half-finished. In fact, he says it was final and had been peer-reviewed.
After it was written, the author says his bosses reassigned him from fisheries to honey. MPI won't confirm this, citing privacy reasons.
Despite attacking the report, even Mr Guy accepts the central premise of it is true - MPI cannot accurately assess the size of fish seen in the footage.
"No camera in the world can do that for size," he said.
MPI says the current video system will "support" prosecutions - but even when all trawlers are kitted out with new gear next year, it says cameras still won't be able to assess fish size.
The report's co-author says improvements are needed or MPI will end up with vast amounts of footage that's of little evidential value.