What is it?
Where does it come from?
How do you get rid of it?
This is commonly referred to as tiger stripes and this happens when your gutters are backed up with dirt our debris and they get rained on causing them to runoff and create tiger stripe patterns.
The best way to get rid of this is to use gutter butter or LA awesome on a scrub brush and clean and rinse them in 10 ft increments so the chemical doesn’t eat though the paint.