http://ecopartybox.com.au/latex-balloon-infoI stand corrected, I was talking about latex balloons (manufacturers claim to break down at a similar rate to leaf matter) however this article is basically saying they're no good and will no longer sell them as "biodegradable"....short answer anyone who sells latex balloons but personally will be sticking to floats from now on...might be worth mentioning driftwood isn't a bad float if you tie it off properly, doesn't spook fish and can cast quite well depending on the wood.
Good luck mate!