Dark Rings on Greens

We have a few greens with areas that look like this on them:

This is a common disease of turfgrass called Fairy Ring. There are 3 main types that can be caused by dozens of different fungi. In most cases no damage to the turf is seen. Only a release of excess Nitrogen causing the dark green circles. These areas have been treated and hope to see a reduction in symptoms over the next few days.