Interesting thread. A few quick thoughts:
1. Soap doesn't belong in backcountry streams, brooks, ponds. Period. I don't care if it's allegedly 'biodegradable." You should do your washing---your pots, your hair, your ass---well away from, and certainly not IN drinking water sources.
2. You should avoid either bathing, swimming, or soaking various parts of your body in water that people are likely to be drinking from. When in doubt, either move well downstream from where people are drawing their water, or wait for a better occasion.
3. People are gonna swim in lakes. They've done this for millenia. Be aware that people are gonna swim in lakes, and treat your water accodingly if you're gonna drink lake water.