Greater Wellington Regional Council (GWRC) will carry out a survey of the underground streams beneath Wellington, where eels or even whitebait species may live.
The city is home to a large network of piped and underground streams, and the council says it wants to know how healthy those streams are and what is living in them.
Greater Wellington Senior Environmental Scientist Dr Evan Harrison said scientists will crawl into the streams and set traps and low-light motion detection cameras to see what fish and invertebrates are there.
"This is the first phase of our underground survey and we'll be focusing on piped streams in Miramar, Hataitai, Wellington CBD and Island Bay," he said.
"It's a trial to see what results we can get, with a view to monitoring other areas in the future."
Wellington City Council Urban Ecology Manager Daniela Biaggio says above-ground sampling of Wellington's streams have shown a surprising biodiversity.
"Our above ground surveys are showing that despite the amount of development and pollution, our urban streams still hold wildlife treasures such as kōaro (whitebait) and tuna longfin eels," she said.
GWRC-contracted scientists recently found a kōaro living in the small Kumutoto Stream near Victoria University - far from the ocean.
Senior Environment Scientist Evan Harrison said "to get there, this fish would have had to climb through piped sections of the stream under the city, all the way from the harbour!
"It really brings home to us the importance of looking after our city waterways to protect the fish that are literally living under our feet," Mr Harrison said.