Seeing yellowstone on foot?

Yes, high summer is the only time it probably won't get below freezing at night. Swimming in the river isn't recommended either, as the temperature is such that only a few minutes is a recipe for hypothermia. Yellowstone in the summer is almost a constant flow of traffic. There is not much in the way of isolation in the summer. In fact trying to find a place to stay could be taxing. I've been there once in mid-June and swore I would never go back during the summer, and never have. We go early spring, and mid-to late September.

I really don't think you're really aware of the distances involved in and around Yellowstone.