I dug a small wild life pond about the size your contemplating. 30' x 45'.
My soil is very sandy and would not have held water without bringing in 2600 pounds of sodium bentonite pellets to line it after digging with my L2501 bucket and box blade.
I also "plumbed" in about 300 foot of 4 inch black plastic drain pipe that collects rain water from my 24 x 27 foot salt box style tractor shed.
I get very little run off due to the very sandy soil so this pond relies strictly on rain water and water diverted from the tractor shed. The math shows I add about 425 gallons of water for every inch of rain fall from the roof of the tractor shed.
Even with our drought in 2022 and severe drought in 2023 the pond has never dried up and normally the water level is closer to "full pool" than not.
Building this small wild life pond on my property has given me tons of enjoyment and hours of trail cam videos. It was one of the most satisfying projects I have taken on. The pond started attracting wildlife long before it was filled.
Good luck with your project and I think you will enjoy as much as I do mine!