get in(to) deep water
To put or find oneself in a dangerous, vulnerable, or troublesome situation or position, especially that which could be beyond one's abilities to resolve. Anthony has been getting into deep water with his creditors; if he doesn't stop borrowing money, they're going to take everything he owns. I think I've gotten in deep water with this master's course—I don't know how I'll be able to keep up with all the work!