On the Middle Fork of the Salmon (Idaho Wilderness) the forest service asks that you pee in the water. With several thousand people going down the river each summer, peeing on the bank would make the 100-mile corridor smell like one big urinal. On coastal streams it rains enough that urine probably ends up in the river either way. I feel that it is only good manners to go a decent way into the brush so that you are not visible from the river to do your business. Respect for each other is what distinguishes us from cattle.