Water disappears when coming close

So I'm working on my latest project that features a (more or less) small lake. Some parts of it are in a 3d skybox and this is where the problems start. Please look at these pictures: http://imgur.com/a/EwBar . When you're far away from the water you can see it (pic 1) but if you get close enough (picture 2) it just disappears. No there is no leak or anything in the map. The water in the 3d skybox is always visible. Ahh and then there's this other thing, so I use these nice red glass texture in my 3d skybox as some kind of barrier to show people where the map ends. This works very well around the whole map except around my lake. As you can see (picture 3) this texture also gets invisible (as soon as the water disappears), which is strange cuz the texture on the left stays. So I have no idea what to do, please save my christmas and help me out with that

For everybody having the same issues I found a solution! The water was inside one of my visclusters, that made it disappear when I came close. I changed the viscluster so the water is outside of it and now it doesn't disappear. For the red glass: I made it displacements, now it shows up correctly.