Something fishy is going on in Christchurch and is baffling authorities and residents alike.
Hundreds of mullet fish are washing up dead in the city's Heathcote River and scientists are trying to find out why.
"We are concerned that this could mean there's something in the waterways killing fish," said Environment Canterbury (ECan) spokesperson, Nathan Dougherty.
The regional council was alerted earlier this week after multiple calls from concerned members of the public.
An investigation is underway including water sampling and fish testing.
So far, they have counted around 300 dead fish, but it could well be more.
"We've had companies approaching us and talking to us about what they've been doing which is helpful," said Dougherty.
"We've got a lot of work going on there."
In the meantime, ECan is urging people to avoid using the river in the Woolston area and to keep dogs away.
Residents 1News spoke to are devastated by the find.
"I'm really saddened to see the dead fish floating all the way up in the Heathcote River."
Another said, "you have another percentage [of people] who just don't seem to care or think they can get away with it."
But Nathan Dougherty said, "people really do value the river so you know we want to protect those values so there's a lot of aquatic life and people enjoy recreating around it."
Five years ago, a cold storage company was charged after leaking ammonia into a Christchurch creek.
Around 2000 eels died and some fish and left authorities spending months getting to the bottom of it.
Now ECan is calling on the public for help as part of their investigation and asking for any suspicious sightings to be reported to them.
"Maybe something has been washed down the stormwater system or maybe someone's had an accident or tipped something."
But exactly what and how are the answers scientists need to solve the puzzle.
SHARE ME