Lusk chimes in...
I have built several beaches for clients. Here's what works best for us, here in windy north Texas.
We build a retaining wall under the water, at least 18" tall, around the periphery of the beach area in water. We excavate the beach area, install shade cloth onto the ground, then backfill with beach sand. Shadecloth keeps the sand from sinking into other soils.
I like the beach to be at least 18" thick, so when weeds begin to grow, you can run a rototiller through the sand to "fluff" it up, and kill the weeds. Some people kill weeds with Roundup.
The retaining wall under water keeps sand from eroding into the pond bottom.
Simple, and works well.

Teach a man to grow fish...
He can teach to catch fish...