I am always shocked at how much crap seems to be in them that you wouldn't expect. I get the leaves and debris from trees but where does all that dirt come from. You might have a little more from the blowing sand I'm guessing? I have a commercial pressure washer that I use for my exterior painting jobs that does a great job of blasting all that crap out of the gutters. Sadly, you have reminded me of a job that I must do. LOL