A documentary due to screen later this month about the plight of the longfin eel features Whangarei's Millan Ruka and his campaign to clean up Northland waterways.
For years, Mr Ruka has been paddling muddy streams in his kayak, documenting pollution caused by cattle allowed to defecate - and the droppings left to rot - in tributaries draining into the Kaipara Harbour.
He is one of the people interviewed in Saving Tuna, on Maori Television at 8.30pm on October 27, about the lifecycle of the longfin eel and those helping the threatened species survive.
Saving Tuna also looks at how iwi, from Lake Ellesmere in Canterbury to the "Tuna Town" of Moerewa in the Far North, are trying to regenerate stocks; while Ngati Hine's Tohe Ashby tells how the eel inspired the design of the legendary Ruapekapeka pa, just south of Kawakawa, and site of the final battle in the northern land wars.
Co-producer Gary Scott, of the Gibson Group, said the eel was an "awesome fish. The first time you learn the story of the eel, you get hooked, which is what inspired us to start the production."
Eels live as long as humans and can grow to be huge - but they only breed once, in a Pacific location, then die.
Mr Scott said the young eels' journey from the ocean near Tonga to the headwaters of New Zealand's rivers was a feat of endurance and navigation.
Eels were also an important food source for most iwi, who dried and preserved them in large quantities during the annual tunaheke [migration].
However, their survival is now at risk due to overfishing in the 1970s, pollution, the draining of swamps and damming of rivers.