Swim

If you like B movies, you'll love it. However, be warned that there is only 1 adult who can act, and he's barely in it. The mother is terrible. When needing to look shocked or scared, she forces her mouth open unnaturally. She screams once, which is also bad. The 3 teens act fine. Grandpa is terrible, despite being in films previously ('screamers' I think). It's available on Google entertainment if you want to check it out cheaper first. The effects aren't good, however I've seen way, way worse