How to make a realistic river

To make a realistic river:

This one is easy...

Enter heightmap mode, and scroll down, so that you make a depression into the ground.

Now, your next selections are at ground level, you want to cover the entire river. Look at the diagram below, // and \\ are representations of the river, the *s are where you should right click to make your selection

 *  //

    \\

    //

    \\

     \\

      \\

      // 

         *

Now move yourself until you are well under the river and right click again. Hit f3 and make the material water.

Your done! Resurface and check it out!

P.S. you may want to use heightmap a bit more on the ground to raise it up above the river, to give the same feel as the "forest" map