This is an Italian fake documentary known mostly because of its great jazzy soundtrack. The soundtrack album is prized by unusual music collectors. The movie is basically just an excuse to show sexy women in bathing suits getting attacked by dangerous animals. (This reminds me of the similarly misogynistic low budget Italian "Giallo" horror films made in that era in which a lot of beautiful women were killed with lots of blood splattered everywhere.) In the snake scene, we first see a black sea snake, then two women snorkeling underwater in bikinis. After a short time, we see what is supposed to be a sea snake pestering the divers. (For the scenes with the divers, they used an eel, not a snake - sea snakes are flattened only at the tail, this creature is flatten throughout the body.) Then the snake (eel) starts to pester the women, eventually biting both of them on their bathing suits. (I suspect that the eel was lured to that part of the diver's body by some type of food placed in their suits.) The women both convulse and die, but not before one of them takes off her bikini top to show the bloody bite mark on her breast. Finally we see a real sea snake swimming to the surface for air.
You can watch this scene on YouTube.