I too hit the spike at confluence yesterday. I live so close it is hard to resist. It was fun, but it was nasty. Another paddler was surfing the last hole at the playpark, flipped, swallowed a bit of water, and then puked a little. He was finished pretty soon after that, and so was I. When I took my gear off, it just reeked this wierd and repulsive smell. I washed my gear and myself thoroughly when I got home.
As for the foam, its pretty nasty too. Foam can be natural from the procucts of decaying wood and plant life. It can also be unnatural if any detergents chemicals or any other crap get in the water. I suspect it is unnatural.
So a nasty day at confluence is still a fun day. I am not sick, no worse for the wear, and had a fun day. Earplugs, noseplugs, keeping your mouth shut and decontamination following the session are a must!