Armed with a machete and a fishing net, wading and crawling, Damian Young and Tom Mansell have explored every nook and cranny of the North Shore's waterways.
Their two-year mission to study the health of the city's 26 streams took them 150km through slushy silt and man-made filth.
But italso yielded unexpected delights - shady fern-banked glades and whitebait galore.
In the upper reaches of the Wairau Stream, the city council's "stream walkers" found banded kokopu - a native fish - and, under a bush canopy in suburban Beach Haven, the giant kokopu.
"There was more life in the streams than we ever dreamed," said Mr Young. The banded kokopu would have had to travel up to 7km through inhospitable, mostly concrete, channels from the Wairau Stream mouth near Milford Marina.
Mr Mansell said they saw a giant kokopu which a resident had adopted and fed like a pet.
A stream running into Browns Bay was an unlikely habitat for numerous schools of whitebait.
Freshwater crayfish were found in nearly every stream where there were shady spots.
The extent of fish life in a city troubled by sewage overflows was welcomed yesterday by environmental consultant William Kapea, who grew up on the North Shore.
"It's a surprise when you consider the development that's going on. But it shows you how hardy those native species are."
Mr Kapea recalled North Shore creeks 40 years ago teeming with kokopu and big crayfish.
In his father's time, he said, children chased hundreds of kokopu into traps made out of fern fronds bound with flax.
Freshwater Fish Society president Dene Andre said banded kokopu had declined over the years on the North Shore because of culverts, silt run-off from developments, contaminated stormwater and sewage overflows.
Data gathered by Mr Young and Mr Mansell will back the city's case for regional council consents to run, maintain and upgrade stormwater and wastewater networks.
