it is a bug that people with AMD graphics cards are having. i am on an i7 and it is still unplayable.
Recent community posts
says "AMD Radeon Graphics / AMD Catalyst Control Center" under what controls it. as far as lag, just struggle into the options and turn the water display settings down all the way and that will fix your lag.
i'm not sure if this is a bug or something else. i just downloaded the game for the 1st time an hour or so ago and nothing i do nor how many times i delete it and re-download it, the skybox or maybe the water is freaking out but it is unplayable for me. (making a video now, one moment)