The "Q-boat" has been brought to New Zealand by the National Institute of Water and Atmospheric Research (Niwa) to test river flows.
It was initially tested on the Clutha, Pomahaka and Taieri rivers and was now being used on North Island waterways.
The boat has an acoustic Doppler current profiler that produces a record of water current velocities, width and depth.
The boat is operated from a river bank using a remote control and the data is transferred directly to a laptop computer.
It was more accurate than using traditional methods for gauging river flow and the results were instant, Niwa principal technician Wayne McGrath said.
"The Q-boat measures the flow, and the relationship between that measurement and the river's water level gives a relationship known as a rating for the river."
Niwa hydrologist Evan Baddock said the boat was just another tool for doing measurements but had the advantage of being able to be deployed in difficult places.
"It's a great tool but its big, cumbersome and expensive," Mr Baddock said.
It would return to Otago at some stage to continue assessing the region's river flows.
Niwa hydrologist John Fenwick, of Christchurch said the boats cost about $20,000.
Fourteen teams around the country were expected to make use of the Q-boat.
Q-boats take their name from the decoy merchant ships with concealed weaponry, used to lure submarines into making surface attacks during the two world wars.
