A dog walker saw two boys use a slingshot to shoot a duck on the Monmouthshire and Brecon Canal in Cwmbran.
She was walking along the stretch by the Pets at Home store on Cwmbran Retail Park in the evening on Friday 24 July.
She told Cwmbran Life: “They sprinted off when they saw me. The poor thing drowned.”
She saw a second dead duck in the water when she walked in the stretch nearer B&Q on Thursday 30 July.
The 24 July incident was reported to the police. A police spokesperson said it appeared to be an “isolated incident” with no other slingshot incidents being reported to them recently.
The spokesperson said: “Officers have carried out patrols in the area as part of an operation tackling anti-social behaviour.”
You can report incidents to Gwent Police on 101 or via the force’s social media channels.