I love open water swimming and use a home made swim float for safety and visibility. They are so easy and cheap to make I give them away to all my swim partners, they all love them! Use a thick type swim noodle cut in half. Thread a thin nylon rope (1/4') through tube and tie it securely to 2 snap cable ties placed near the far end. Extend the rope approx. 4 feet past the other end, and tie free end securely to a short length of bungee cord looped to go around your ankle. For extra visibility I cover snap ties and a few other places on the noodle with bright colored Duct Tape. The swim noodle trails behind you and does not interfer with swim stroke or kicking. You can sit on the noodle, rest with it under armpits or use it ti aid another swimmer. This costs less than $5 to make.
Thanks for the advice, very useful.