When I was a child the main drainage dyke from the nearby town ran past our village into the tidal river. Many houses along the way simply piped wc effluent straight into the dyke, as did most of the houses in the town although a lot of houses had chemical toilets still.
As children we donned Wellington boots and caught sticklebacks in jam jars in the dyke. Even at that age we knew what the bits of paper and brown lumps were. We avoided them. Somehow no one caught any interesting diseases despite the dire warnings from parents. We built up immunity.