They were reported by a member of the public and found by Walmsley Bridge on Yass River Road.

Yass River flows into the Yass water supply, but the council's director of engineering Stan Robb said the dumping had not created a public health issue.

It's not understood who or why someone would dump the kangaroos in the river.

The council will be responsible for removing the carcasses and is having to source specialised equipment to do so.

The council has warned residents it is illegal to dump animal carcasses in the river.

An individual can be fined up to $4000 for this kind of action or $250,000 in a serious case if it went to court under the Protection of the Environment Operations Act, Mr Robb said.

It seems a bizarre act, considering landholders can legally cull kangaroo populations according on their property size.

The red tape surrounding kangaroo culling was relaxed by the NSW Government in August 2018.

The new limits for eastern grey, western grey and red kangaroos under the "licence to harm" rules are: 50 kangaroos from one to 40 hectares; 100 'roos from 41 to 100ha; 250 'roos for 101 to 500ha; 500 'roos for 501-5000ha; and 1000 'roos for 5001ha and more.

Landholders still require a licence from the National Parks and Wildlife Service to shoot kangaroos, but can apply for a licence over the telephone or via email.

More shooters can now also operate on a property under the same licence and carcasses no longer need to be tagged and left in the paddock.

Landholders are further able to use the carcass for a range of non-commercial purposes such as bait meat.