Lake Lurker

Lake Lurkers are spirits who, as the name strongly implies, lurk within the murky depths of a lake (or any such body of water). They wait for people to go into the water, then drown them to feed off of the escaping life force as they suffocate). 
Lake Lurkers can affect the water itself, sending out water tendrils to attack or drag victims into the water. The more powerful Lurkers, after killing a target, can take possession of the body for awhile, using it to leave the body of water and attack others on land.