It has been described as a mini Kakadu because of its important biodiversity, but someone with “malicious” intent is repeatedly vandalising the fence to let dogs into Altona’s Truganina Swamp.

Letting dogs in has also let in rabbits and foxes, which threaten migratory birds from as far as Siberia and endangered species, such as the Altona skipper butterfly.

Melbourne Water’s waterways and land officer Gerard Morel is at his wits’ end.

He said the 2.7kilometre fence had been cut in 18 places most recently.

“We just finished repairing them on Friday and, since Friday, there’ve been at least five new cuts,” he said while inspecting for new holes. “So, there’s some really malicious people, or maybe it’s just one person, around here.”

So malicious in fact, that the wire of an unlocked gate was cut.

Altona North police have been notified about the vandalism and will conduct patrols.

Secret cameras have also been installed.

The vandalism has Melbourne Water stumped as dog walkers have plenty of room outside the fenced-in area, which is a bird refuge within the flood-retarding basin. Almost by accident, it became a conservation area to protect endangered wildlife.

“I call it a little cold Kakadu because it’s a semi-aquatic environment that used to cover a much bigger area of Altona,” Mr Morel said.

“They’re letting their dogs run in, which disturb the birds, and maybe they won’t breed or they’ll be too weak to fly back to where they came from.

“But also it means foxes can get in, potentially wiping out the birds that are nesting on the ground. Rabbits go in there as well and eat the chaffy saw-sedge, which is the food plant of the Altona skipper butterfly, which is found nowhere else in the world.

“There is so much other room in this massive park for people to walk their dogs.”

One migratory bird that rests there, the Northern Siberian bar-tailed godwit, loses half its body weight flying 11,000 kilometres to Altona. If disturbed by dogs, it may never make a home. Report vandalism to police.