The Department of Conservation will reconstruct the scene where an environmental activist photographed two men he alleges were illegally fishing.
A photo on the social networking site Facebook shows the men with a car and boat at the water's edge at Long Bay marine reserve near Auckland.
Pete Bethune, who posted the picture, says he has identified the men and has passed on the photos to DoC, which is investigating.
DoC biodiversity programme manager Phil Brown says staff will recreate the photos on Friday by matching them to geographic landmarks at the reserve to find out whether the men were in fact within its borders.
Mr Brown says the department welcomes Mr Bethune's actions.
Illegally fishing in a marine reserve can incur a $10,000 fine and three months in prison.