A dog owner has been left a $700 vet bill after her pet ate one of the more than 200 dead eels found washed ashore at Ōrākei Basin, while scores more eels have been discovered floating in a second Auckland waterway.

About 180 dead eels have been found in a stream in Wattle Downs, with local leaders saying ammonia poisoning is behind the mass fish deaths.

Sarah Walsh-Devoy said she wants to warn others of the danger of dogs consuming the dead eels after her miniature schnauzer Elvis made a costly mistake.

Walsh-Devoy said she was letting Elvis run on the off-leash area on Monday when she saw him rolling in something.

“He was trying to eat it, it was disgusting ... the smell was so bad.”

When they returned home, Elvis, who was usually under everyone’s feet, hid away from the family and refused to eat or drink.

Walsh-Devoy said she rushed her pet to the vet when he began to vomit “white foamy stuff”.

“They were not surprised when I said he had tried to eat an eel.”

The eel’s small bones had scratched Elvis' oesophagus. He was able to be taken home straight away with pain relief, antibiotics and a $700 bill.

A cyclist on a late-night ride at Auckland's Ōrākei Basin says he found more than 100 dead eels washed up on the shoreline. Photo / Pete Mazany

She also had to buy a special shampoo to get the rotten eel smell out of Elvis' fur.

180 dead eels in Wattle Downs stream

While the death of the 201 eels at Ōrākei remains under investigation, the death of more than 180 of the creatures in a Wattle Farms stream is more clear-cut, with Auckland Council saying the two incidents are not linked.

Manurewa-Papakura Ward Councillor Daniel Newman, who lives locally, said the eel deaths were the result of wastewater overflow.

“I am informed that the dead eels are likely to have been the result of a wastewater overflow as the council got a positive ammonia result, upstream of the ponds.

About 180 dead eels were collected from Wattle Downs.

“This is particularly outrageous given the long dry period – there has been no significant rain that might otherwise have triggered infiltration into the stormwater network.”

He said it was essential that “residents remain vigilant” for many contaminants in the water network.

Row Robinson, who runs Pest Free Wattle Downs, said the stream passes through many commercial spaces so there is a big risk of contamination.

He said stormwater from Manurewa village commercial areas, roads and carparks drains into this stream.

The Auckland Council head of operations for healthy waters, Andrew Skelton, said a contractor removed the dead eels yesterday in Wattle Downs.

“We do not have any reason to believe that this incident is related to the dead eels found last week in the Ōrākei Basin.”

Pete Mazany was biking around Ōrākei Basin on Thursday evening when he discovered numerous dead eels lining the basin’s shoreline.

He said he counted more than 100 longfin and shortfin eels lying dead and noted a “smell” while filming the scene.

“These eels are the canary in the coal mine. We know that they die when the environment is imbalanced.”

Rachel Maher is an Auckland-based reporter who covers breaking news. She has worked for the Herald since 2022.