What about the van underwater?

Perhaps it was symbolic of nature "swallowing" them up. Traces of Peter and Marcia may have met the same fate after their demise. Throughout the movie, there is a sense that the woods they drive through to get to the beautiful beach is in control of their fate more than they are. Maybe the sea lapping at the beach below their camp is similar. I agree, though. Great movie. Ever see Burnt Offerings?

I thought that one of the people from the van filled the girl by mistake just like the John Hargreaves character did and pushed the van into the ocean to hide it as they thought they were alone.

In the remake it was a murder suicide, this is kinda what I though maybe on the first one, that the animals drove them mad and they ran it into the sea.

The film was extremely haunting and the remake was very good, it kept me awake that night!

I read your post before watching the movie and I tried to pay extra attention to what was going on there but like a lot of the movie it doesnt make sense and is left unexplained.

At first when we see the van it is a ways downe the beach, it is parked very close to the water, and we see no human activity...in fact it is parked so close to the water if the tide comes in, it could get drug into the ocean....or maybe it was driven in....but we dont know...

is their even a body(s) in the van when he goes out to take a swim? I couldnt tell if it was a doll or a little girl, but upon review I think its a doll.

So wait, I skipped ahead a bit, we need to go back to before he swims out to the van, he finds the camping spot, but the camping spot didnt look like a camp spot, as more of they were living there, but once again, I could be wrong...and then there is another dog, a very angry, unhappy borderline rabid pet dog he finds and then leaves in the girls tent.

Nothing ever gets explained, but if you follow the rest of the movie I believe we are to assume the same tragedy happened to these other people whom we never see.