The weather was sunny and there were lots of people walking, swimming and fishing at Lake Esmond on Saturday.

Julie* had been walking around the lake when she said she was disturbed by an "awful" act that unfolded in front of her eyes.

After walking several laps, she noticed three young males who were listening to loud music, fishing and drinking beers.

While initially annoyed seeing them throw their rubbish into the lake, it was when she sat down for a rest that she noticed one of the young men start to throw rocks into the water.

"I was unsure if he was skimming rocks or throwing them at something," she said. "Then I stood up and saw a family of ducks."

At the same time, she said the man yelled out "I got one", before running up the bank and gathering more rocks to throw at the ducks.

"He proceeded to throw them at the ducks and then waded into the water and pulled out one of the ducklings, threw it around then beat it to death with his sneaker.," Julie said.

Julie told The Courier the incident occurred in front of about 20 others, including children.

In shock about such cruelty being inflicted on an innocent creature, she and three men confronted the young men.

She said one apologised while the other two tried to hide their faces, before they ran off.

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Julie said the mother duck was desperately trying to revive her baby and it was distressing for everyone.

"It was a thrill kill and ruined a lot of people's day, not to mention the poor ducks," she said. "I believe if we hadn't stopped them then they would have killed all the ducks as they were still throwing rocks when we confronted them."

Julie reported the alleged incident and has handed over video and photo evidence. The Conservation Regulator is currently investigating.

Manager of Regulatory Operations in the Grampians, Brian Hamer, said all native wildlife was protected in Victoria and it was an offence to kill, take, control or harm wildlife under the Wildlife Act 1975.

Severe penalties (including imprisonment and fines) apply to those found guilty of an offence under the Wildlife Act.

Animal Justice Party MP Andy Meddick said he had heard about the allegation of animal cruelty involving a duckling at Lake Esmond.

"I understand it is now being investigated and if what I hear is true and proven then the full force of the law should be brought to bear on the perpetrators."

He said if the allegations were true then it was a clear animal cruelty breach and should be prosecuted under POCTA, which allows heavier penalties, rather than under the Wildlife Act 1975.

*Julie is not her real name