Title says it all
Ok, first step is to press escape. It gives you the option to go to Options or to Quit. Click Options. You will see four tabs, Interface, Video, Sound, and Controls. Click Video and scroll down until you get to View Distance. Drag it to zero. You can still be able to see, but not as far now. But that is not all. Scroll up until you get to Water Reflection. Click it, then uncheck the box. This next part is optional, so you don't need to do it. Scroll up until you see Rendering Subsystem. Switch it from OpenGL Rendering Subsystem to Direct3D Rendering Subsystem. It will tell you to restart the game, so exit all the way out then come back in. The terrain will all be the same, but hopefully all dat lag will be ridded of!