Hi, I ran the "Adjust Flow Direction in Streams" tool which worked fine. When I try running the flow accumulation with the adjusted flow direction grid as input, it only works when I run it for a small area but not for the entire area of interest. But if I run the flow accumulation with the regular flow direction grid (not the adjusted one) as input, it works fine (even for the large area). I'm using ArcGIS 10.1. Any idea why that is? Thanks for your help, Maria.