Look at
Pond Dam Piping for several ideas.
Welcome to the forum!
If wanting to swim, and not get nipped by fish, don't stock Bluegill or hybrids. Fathead minnows Yellow Perch, Smallmouth Bass and Redear Sunfish would do well to keep snails, mosquito larvae and leeches in check.
If you don't mind an occasional nip, or like more warm water species, bluegill and largemouth bass are hard to beat!
With a creek close to the overflow, I'd try making a straight through overflow pip have at ;east a 6' drop from pipe to ground, or whatever fish are in the creek will soon be in your pond during any high water/overflow event.
