Judge Chris Field deemed that "entirely appropriate" and did not impose any further penalty on top of the conviction.
"They've (DoC) taken this very personally and have been supporting them (Mr Muncus-Nagy's family) in a number of different ways."
Judge Field said there were several areas where DoC failed to ensure the safety of their employee.
It could have sent a second person with him to carry out the work, and ensured he had a life-jacket or personal locator beacon, he said.
"These are some practicable steps that DoC could have taken in this instance."
Judge Field said Mr Muncus-Nagy's death had "dramatically" affected his wife's life: "She is daily reminded of his absence and feels an ongoing sense of loss and grief."
Speaking outside court, DoC's deputy director of operations Sue Cosford said it had strengthened safety procedures on Raoul Island since the incident.
"We've instigated a significant number of improvements to ... ensure our people are safe when they are working on the island. In the case of this particular activity on Fishing Rock, we are no longer doing water temperature testing there.
"This was a truly tragic accident. We greatly regret Mihai's loss, it's been very devastating obviously for his family and for our team here. He was a really well-liked, respected member of the team."
A plaque had been erected on the island in Mr Muncus-Nagy's memory.