[up the creek] or [up the creek without a paddle] {adj. phr.}, {informal} In trouble or difficulty and unable to do anything about it; stuck.
* /Father said that if the car ran out of gas in the middle of the desert, we would be up the creek without a paddle./* /I'll be up the creek if I don't pass this history test./
Compare: DEEP WATER, IN THE SOUP, UP A TREE, OUT OF LUCK.