It's hard to tell what is in the picture. I see lesions on some of the grass blades. That's not good. Is that a fungal mass under the canopy of the grass? Usually the big ugly fungal masses are harmless and go away in a few days. They are just an ugly form of mushroom. Have you been overwatering the area? What has your watering regimen been?
And what kind of grass is that? Looks like St Augustine but it's easy to get fooled in these pictures.
Where do you live?

Hi -
I live in NY, Long Island.
The grass was sod I bought 3 years ago, and its KY bluegrass from memory.
I water every other day, for 15 minutes in that area. But I remembered that that area is also where i dumped the kids swimming pool daily during the summer months.
That is definately fungas under the grass. I can zoom in the picture and see it clear as day. i was wondering is it a specific fungus and is there a specific treatment for getting tid of it? It is definately spreading. I am turning my in ground sprinklers off from today. Should i see results of this going away in the next few weeks? What if i don't? Can i dig it out? Is there a treatment?
Thanks!

This time of year in your area you should be watering a full inch, once every 3rd week. The fungus is there because you are watering too frequently.

You cannot change your watering regimen cold turkey. Start by putting out some tuna or cat food cans and time how long it takes to fill them. That is the time it takes your system to apply an inch of water. Mine takes 8 hours but my neighbor's takes 20 minutes. Every system is different. You have to measure your own. So if you do that test, then you have already watered a full inch and you don't need to water this week. But watch your lawn for signs of dryness. If any part of it it gets dry before 3 weeks is up, then water again immediately for the full inch. It will probably go a full week the first time and then need water. The second time it might go a full 2 weeks. Next month you will not need any more water for the rest of the year, but I always try to water my dormant lawn once a month in the winter. It helps the soil microbes. Then next spring, as the temperature warms up, you can reduce the time between watering. Move it up to once every 3 weeks, then 2 weeks, and finally in late June, you will be watering once every 7 days.

The reason for deep infrequent watering is to allow the surface of the soil to completely dry out. This prevents weeds and that ugly fungal fruiting body you got there. It will go away by itself when it dries out. You don't need to put anything on it. In fact, DON'T put anything on it. Fungicides are horrible for the health of your soil. All you have to do to control disease and most weeds is to water properly.

That is a lot of information, more than I bargained for but it's great!! Thank you. I will do the tuna can fill up and follow your guidelines.