Answer:
It seems I was mistaken. Based on your description, you might be thinking of "The 5th Wave". In "The 5th Wave," there is a scene where people are taken by what they believe are rescuers but are actually part of an alien invasion. The characters are not underwater or floating, but the scene where people raise their arms thinking they are being saved could match your description.
If this doesn't match, could you provide any more details about the plot, characters, or specific scenes? That would help narrow it down further.
