Football-sized goldfish, once loved but now thrown away, hauled out of US lake

Huge goldfish the size of footballs have highlighted the danger the once-small household pets can pose to lakes if owners toss them into waterways.

Remarkable photographs posted by officials in a Minnesota city show a number of swollen goldfish, some the length of an adult's forearm, hauled from the local lake.

"Please don't release your pet goldfish into ponds and lakes," Burnsville city officials pleaded on its municipal Twitter account.

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"They grow bigger than you think and contribute to poor water quality by mucking up the bottom sediments and uprooting plants."

Burnsville officials surveyed a local lake after residents complained it was infested with goldfish.

"You see goldfish in the store and they're these small little fish," Caleb Ashling, Burnsville's natural resources specialist, told The Washington Post.

"When you pull a goldfish about the size of a football out of the lake, it makes you wonder how this can even be the same type of animal."

Goldfish are known to cause problems for native freshwater fish and natural habitats if introduced into waterways.

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In 2017, a study from Perth's Murdoch University thrust the issue of giant goldfish wrecking lakes onto the news agenda in Australia.

The Murdoch University study, which included photographs of goldfish which had ballooned to 2 kilograms, said the fish disposed of by once-loving owners were choking waterways.

Goldfish stir up sediment on the bottom of lakes and waterways because of the way the fish feeds.

This movement can suspend nutrients in the water, which can result in algal blooms and choking of waterways.

Goldfish, which are extremely adaptable, also eat aquatic plants and the eggs of other fish, and carry disease.