The woman said it appeared the youth, who was in a group of three, had fished the eel out of the area and he was trying to kill it.
The woman was taking her dog for a walk along the stream last Tuesday, in an area adjoining the Lincoln Medical Centre grounds on Kildare Tce, when she came across the incident.
It appeared the eel, about 50cm long, was in distress as the youth, aged about 19, alternatively picked it up, dropped it onto the ground and jumped on it.
He was with two teenage girls, one of whom appeared upset at his actions.
The woman yelled at the group to put the eel back.
At first the young man laughed it off, but some moments later she noticed him return it to the water.
“It was pretty awful, to experience some cruelty to an animal like that,” the woman said.
Commenters were horrified and some called for the incident to be reported to the correct authorities.
Selwyn District Council group manager property Douglas Marshall said the behaviour witnessed by the woman was unacceptable.
“Eels are a precious native species and we’re lucky in Lincoln to have a place where people can see them up close.
"We would encourage Lincoln residents to look after and care for these creatures,” Marshall said.
In spring, the district council put signs up at the L11 River in Lincoln after teenagers fished and harassed eels there.
About 20 tame longfin eels, protected by the district council’s parks and reserves by-law and also the Reserves Act, raise their heads out of the water to take food from people’s hands.
But teenagers had been seen by residents trying to hurt the eels.
Marshall said anyone witnessing such behaviour should immediately phone the district council on 0800 Selwyn (735 996).
An SPCA spokeswoman said animal cruelty and violence in Canterbury can also be reported to the SPCA Christchurch Centre - 349 7057.
“Police also have the power to enforce the Animal Welfare Act,” she said.
Animal welfare concerns can also be reported online to the Ministry for Primary Industries.
