Terragen 4.5.60, Pixelmator Pro 2.2
Ducks flying courtesy Roger Chapman @ https://unsplash.com/photos/7zj6mKkh-L0
Duck models by printable_models @ https://free3d.com/user/printable_models
Trees by moonikoffice @ https://www.cgtrader.com/moonikoffice
Vegetation by Maxtree @ https://maxtree.org/
Water lilies by asmodeus88 @ https://www.cgtrader.com/3d-models/plant/other/water-lily-05dbf419-5486-4eb1-897e-23527a49bef3
Also available @ https://www.deviantart.com/jhmartinez/art/A-Quiet-Little-Pond-898044898