Once in a while we'd get mud like debris on our patio. Thinking maybe a bird or our gutter needs cleaning? Had lots this morning after some heavy rain yesterday afternoon but nothing straight after the rain?
Moss, crud out of the gutter? Just cleaned out gutters here, we have blackbird who get in the gutters, & has a good rumage looking for worms etc & throwing everything out onto path below in the process, amazing the amount of crud in them, the gullys were just as bad.
I hope you will forgive me for saying this but if that's all you've got to worry about you are very lucky. As you get older you realise that even the odd bit of dirt has it's place in the world and who are we to displace it? You could always blast it away with a pressure washer.