Looking for name of a movie about a group of girls that go camping on a boat. I can remember beginning scenes?

I had work in the morning and was unable to finish this movie. What I remember that happened was a girl gets abducted in the beginning of the film but I don't think she was killed. Then the movie flashed forward I think like 12 years but not sure about that. But anyway the part I left off on the older woman whom was in charge of the younger girls gets murdered by this man and woman. She is tied up and thrown into the water. Then the killers try and hit the girls that are swimming in the lake with their boat. I hope this makes sense. If anyone could help me that would be great, I would like to finish watching this and see how it ends. It was on a streaming site so unfortunately I can't look through history to see what it was and I tried messaging someone but they weren't much help.