Nic witnessed the man shooting at the geese in the smaller lake at Westlake Reserve in Halswell about 10am on Tuesday, January 30.
She posted her concerns on social media.
“I noticed a man standing close to the water near the rocks. The man, who looked to be in his late 60s, seemed to wait until none of the 20 families were walking past before shooting his slingshot.
"He advised me, when asked, that he was “keeping the dirty f**kers away”.
The post created “quite a heated debate”, Nic said.
It has since been taken down as the man was “identified and later threatened” by a member of the public.
The large light-brown geese with a white chinstrap are afforded some protections under the Animal Welfare Act 1999.
Nic sent the SPCA a letter of concern and a spokesperson responded, saying the information provided was not sufficient to progress an investigation.