all that achieved was the end of the route ( much of which is below sea level due to the original dem being lowered so much) , is now an inland sea and i cant adjust the water height. However on the plus side the terrain looks ok under the water. Except that once i wander around a bit the dodgy terrain rendering returns . Any ideas of how i can get the water to lower ? should i try again and make the water level lower in both route and merge beforehand ?