Ken Willard designed a number of small float planes one of which was the Pond Hopper. I believe it had a 23" wingspan. Power was a Pee Wee 020. I started to build on but micro electronics were not available back then. It would be a great one to try these days.
I saw one of his other designs a few years ago when I went out to BC. It was even smaller and it flew well although from a handlaunch.
Peter