Great idea! There is this guy who quit his job to float along rivers with his bicycle and fish out plastic. His design has 2 pontoons - maybe you could design something similar which could be unfolded and inflated on the go?
Dhruv Boruah, a cyclist and environmentalist from London, found a way to make his bike trips much more than a fun pastime or good workout. He combined two of his passions and found himself riding his bike on … the city’s canals. Boruah decided to learn how to make his bike float on the surface so that he could ride it on the waterways and collect plastic trash – and the results of his “Thames Project” are inspiring in every way.
http://www.onegreenplanet.org/news/m...-plastic-trash