Sand beaches in fresh water ponds turn into a slimy mess if you don't keep up with the maintenance.

I put a gravel beach in my pond. The dog likes it, the RES like it, and it's good for putting the boat in.
It's also really good for growing FA (snot grass, pond scum, green slime). I rake it if the grandkids
want to get in and splash around. That's not a pleasant task for worn out old man.

Everyone here prefers to use the dock for getting in/out of the water when swimming.

That said, if I was really serious about having a swim beach I'd start by laying some sort of geotextile
fabric, then come with 3"-4" clean chat rock, top that with 3"-4" of man-sand, and stock up on
aquatic weed killer and algaecide.