I can't remember what scary movie this is!?

These couples decide to go to a lake, but while they are there they keep being followed and eventually killed. only 2 i think survive. I believe a brother and sister are the ones killing everyone. the people try to escape through out the forest and get killed in really random ways, like some pointy log things running over them. i thinnnnkkk it is an old-ish movie, but don't quote me on that! i really want to remember it cause me and and my friend watched it on comcast on demand and we can't remember what it was! please help!! thank you!! :)