What is this? photo

[rkeith]

Great comments everyone, thanks! The ventilation was OK (two large box vents on each slope and soffet vents). The leak was not visible from top of the roof, I missed it until I got into attic.
Thanks,
Rusty

[sturetsky]

This is my first time posting on NACHI, I would like to say hello.

Is this the only area that is affected? Unless it is widespread I would not jump up and down screaming mold and reccommending "tear out the roof".

As David and Caoimhin advised, get the leak fixed. If I was really concerned I would suggest cleaning and monitoring. If you want to use the words "licensed mold remediator", you could. But, in my head any handy man could clean it up.