The streaks are normal dirt carried from the asphalt shingles on the roof.
It took me about two years to realize I had a blockage underground.
Anyway... I'm left with these streaks on the face of the gutters. Spraying
with 409 does fair but wiping it with industrial strength bleach, then 409,
then bleach again does the best and nearly removes the streaks completely.
Anyone have a better suggestion? The gutters are aluminum with - I presume -
a powder coated white surface.