Here is a closer image (as close as I can get).

Clearly (to me) a fungus. If you zoom in close you can see spots on the leaves. A dark brown spot is surrounded by yellowish and then green.

Where do you live?
What is your normal watering routine when it is not raining (frequency and duration)?
When were the last 2 times you fertilized and what did you use?

Get a bag of Headway G or Pillar G and apply it every 28 days, it will stop the fungus on its tracks.

One of the Internet grass gurus just tapped me on the shoulder to say it probably was not a virus because it was too even looking. He suggested it looked like the natural state of fine fescue when it becomes heat stressed.

Can you post yet another picture even closer than the others. It helps if the pictures are taken in shade or under clouds. I have used my body to make shade to take pictures.

Sorry for the delay. I've been treating the lawn with Spectracide Immunox every two weeks. It seems to be improving somewhat but still does not look healthy.

This photo is the closest I can get with my camera.

I'm in Knoxville TN. I have an irrigation system and was watering 3x/week in past years. This amounted to about 1"/week. This year I have not watered at all...we've had that much rain.