Rare longfin eel have been found in a Christchurch wetland that opened last year. (File photo)

Endangered eels (tuna) are among the wildlife that has moved in to a Christchurch stormwater catchment.

A metre-long longfin eel, about 50 years old, was among the 15 fish found in a wetland opened by the city council in Mairehau last year.

Ecologist Greg Burrell led the fish salvage, which happened while minor repair work was done. He said finding a number of large eels in the open area was a surprise and showed they had rapidly colonised the new wetland.

"Bigger eels don't tend to move around much day to day, tending to stick within a small home range, so it's neat that they're moving in there."

Council land drainage manager Keith Davison said the wildlife in the wetland suggested water quality was good.

The stormwater catchment holds water running off about 20 residential hectares.

Longfin eels are deemed to be at risk and declining. The Department of Conservation recommends people avoid catching them, or return them to the water unharmed if they are caught.