Devil's Pond
(2003)

Julianne (Tara Reid) comes to realize that her husband Mitch (Kip Pardue) is bound to kill her; he has sunk their boat, restrained her to a chain and terrorizes her.  So she decides to fight back, and forces with him, trying to escape.  Finally, she blows a hand off him with the shotgun, and then, retrieves the key to open the headlock and release herself; she then restrains the shotgun's trigger and leaves Mitch to die.

Then, she swims across the pond to the other shore. In the end, she finds the abandoned truck, where she leaves her wedding ring on the door's lock, and walks off, safe.

Thanks Dr. Mat!