There are a few designs and production models for backpack frame and inflatable pontoons that can be attached to your bicycle. I have looked into
into pedal bike/boat combinations as I live in the city. I even saw the Schillar prototype bike boat on the Hudson once. All interesting but too complicated. Unless you have a dedicated paddle boat, I think the efficiency might be too low and it's rather cumbersome to carry around all the material. I had an inflatable boat that I biked to the Harlem River to paddle in but had to return to my bike and trailer to get back home.