Scientists, researchers and school students who travelled to the remote Kermadec Islands had to stay on their boat when they got there, because the Department of Conservation (DoC) wouldn't let them on land.
The groups arrived home yesterday after hitching a ride on the navy ship HMNZ Canterbury as it went to resupply a DoC station.
The journey to the Kermadecs took two days and nights, but those aboard had to spend nearly a week docked off the coast.
Some involved have told RNZ they were annoyed they could not go onto Raoul Island, Rangitahua.
But DoC northern operations director Sue Reed-Thomas said the priority was to service the DoC station and that took longer than expected.
That meant DoC staff were not free to carry out the strict biosecurity and health and safety supervision needed for others to come onto the island, she said.
"We tried really hard. A number of things conspired against us to get the essential work done and look for the opportunity to get people on the island - including the weather and equipment failures and the need to leave earlier than planned," she said.
Since myrtle rust was found on the island last year, biosecurity was much stricter, she said.
The students on board were there as part of a Sir Peter Blake Trust youth expedition.
One of the leaders, Mark Orams, says it was a tricky balancing act for DoC.
"Many of us would like to go into and experience these really pristine, remote locations but in doing so we can put at risk those very things we're interested in seeing," he said.
The students had always known they may not get on the island and still had a great time, he said.
They helped the marine scientists on board, swam, snorkeled and went out in helicopters or smaller boats.