Maria Shriver called 911 herself -- calmly -- when her son Christopher Schwarzenegger was injured in a boogie boarding accident in Malibu last weekend.
Maria told the operator, "He can't move off the beach ... maybe like a broken ribs or something like that."
She explained, "It's my son ... he's awake and breathing .... he just can't move. He's having trouble breathing."
Christopher was taken to a nearby hospital, where he was treated for multiple broken bones and a collapsed lung. We're told he's going to be OK.