I saw this movie when I was a kid in the early 90s. Im positive its release was no earlier than the late 80s. My memory of the film is vague, but these two sisters.. probably 11 years old.. go ape s**t and start killing. The only scene I remember some what in depth is at the end one sister sends the other running into the ocean while she sprays her from behind with bullets. I emailed Joe Bob Briggs about this one. He had no idea what it was.
Was it an American indie or a foreign film? Reminds me of DON'T DELIVER US FROM EVIL, though that film is much older and ends with a shocking - not ocean related - ending. But shares similar themes.