In Australia it means that you're in a lot of trouble, with no foreseeable way out.
"Oh man, I can't believe I lost my paperwork; that stufftook me hours and it needs to be in by tomorrow!"
"Sounds like you're up shit creek without a paddle, mate."
To be in a bad situation which is either slowly or rapidly getting worse with no evident way out. Should you be armed with a paddle, you still, typically, have a slow long recovery