The phrase is of unknown origin but it seems that it comes from the "franchise" of Star Trek porn parodies such as "Sex Trek: the next penetration" and "Where no man has cum before".
Fred: Hey, you know what? I slept with Janice last night!
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.
"Base we've got some square groupers floating outside of Miami harbor."