Glad you asked...
You can make a fake river, stream or creek by digging a long downhill trench and scatter some big rocks in the trench. Place a water hose at the top of the trench turn on the water and let it flow.
Then again, this answer might help you...
Making a fake river just requires a bit of imagination. You could use foil paper, crinkle it and add white sprinkles to replicate the flowing water. Make sure you use a brown base. You could add rocks and greenery to enhance the scenery. You can also purchase water kits used by hobbyist to make fake water.

