Goldfish are commonly found in children's bedrooms happily swimming around in a glass bowl and generally looking gormless.
But bizarrely there is also a booming population of the fairground favourites in Vinegar Pond on Mousehold Heath.
Experts believe the fish were dumped in the water as unwanted pets but have bred over the years.
And goldfish that are not constrained by a tank grow big - some folk who have spotted the Mousehold fish think they could be as long at 14inchs.
But the goldfish - native to East Asia - can't stay because they are causing havoc to other native species.
Councillor Gary Champion of Sewell Ward said: “The introduction of fish to the vinegar pond on Mousehold Heath, while possibly well intentioned, has had unforeseen repercussions.
“Due to the extreme hot weather, the water level is incredibly low, causing concern about oxygen levels and therefore additionally resources will have to be spent to transfer these fish to another location.
“It is incredibly important to highlight that releasing any animal into to wild is not advisable without expert advice.”
One of the biggest impacts has been to tadpoles numbers because the goldfish have been feasting on frog spawn.
Gary added: “In order to protect frog numbers from decreasing, wardens will be monitoring the pond to ensure frog spawn and young tadpoles are not being decimated by fish in future years.”
Kevin Murphy, founder of Norfolk Wildlife Rescue said: “It poses risks for the wildlife.
“But I am always shocked by people who disregard the life of the animal they choose to care for, they think they are just so easily thrown away.
“No animal should just be dumped in an environment that isn’t suitable for them.”
Kevin said there are many organisations that will take unwanted fish in and that the people responsible for dumping their fish in the vinegar pond should come forward so they can be educated.
He added: “I do this as a volunteer, I like helping animals but so much of my work is just cleaning up other people’s mess.”
Goldfish: The facts
Native to East Asia, goldfish were first bred for their striking colour more than 1,000 years ago in Imperial China.
They are a member of the carp family and released into the wild have been known to become meddling disruptors to eco-systems in parts of North America - and now in Norwich.
Displaying schooling or swarm behaviour, the animals are known for copying themselves in mirrored surfaces.
Goldfish have one of the most surveyed senses of both hearing and vision in all species.
The largest goldfish on record measured a whopping 19inches and was aptly named Goldie.
In their homeland of China, goldfish are seen as symbols of good luck and were so coveted that only members of the grand Song Dynasty could own them.
It is wrong that goldfish have bad memories - in fact they can recall things as long ago as three months.
Additional reporting by Kai Double
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