the worst smell i ever encountered was when i worked at a cemetery and flooded/sunken graves had to be excavated.
i was fortunate not to have to work directly on this task,but just driving down the road the dirt hauling trailers had dripped a thin track of water on in passage(hours earlier)made me gag.
the stock wisdom when doing this task was, "don't plug you nose unless you want that taste in your mouth a long time."
definitely the worst smell i've ever encountered.