Something I noticed while switching to city life after a while of living on nature is how little dirty you get on nature compared to city life.
Also, if you avoid crap food (not gonna expand on that now) even your sweat will smell good!
Please don't use ANY kind of soap while on a river, lake, sea or whatever. It doesn't matter how bio \ Eco \ hippie recommended it might be, there is NO soap that would not fuck up badly (the main ingredient on soap, so that it can clean you is the responsible, nothing else)
I have a small brush that I use both for body and clothes that does wonders without soap, I can even see the dirt being peeled out of my skin. That iis a traditional way of cleaning yourself without soap that, in my opinion, is better than soap. There are some sponges made out of roots or dried pumpkins or other veggies that have the same effect. Try it out with a steam bath and feel reborn!
Also, I don't know anything about getting sick for not being clean, and I say that backed up by long long time without showers.