The mushrooms are a good indicator that the soil is getting way too much water. Once the seed germinated, you should have backed off on the watering frequency and gone up on the watering duration. For example for new seed the recommendation is to water for 5-15 minutes, 3x per day, for 2 weeks until you get about 80% germination. You never want the soil to be mushy, so that's the reason for the 5-15 minute range. All you need to do is keep the very surface of the soil moist continually. For fescue the normal germination to 80% is 2 weeks on the average. After that you should drop back to watering once a day for, say, 20 minutes, and see how that goes. Again, no soggy soil, ever. After a few days of that the roots will be growing, and you can back off to watering every other day for 20 to 30 minutes. When the grass gets up to 5 inches, you can mow it back to 4 inches and back off on watering again. They tell me in Idaho it doesn't get that hot in the summer, so watering once a week should be plenty of water. I live in San Antonio, and once a week is enough for established turf in full sun.

The idea with watering deeply and infrequently is to develop roots that will dig down deeper into the soil to find the moisture. If you water every day, then the roots will stay near the surface where any sudden heat will affect them more than if they were deeper in the soil.

Now would be a good time to reseed if you think it needs it. But also, if you think a fungus got to the lawn, you should check with a local garden center to see what they recommend for your situation.

I always like to through in a plug for organic fertilizer. I use alfalfa pellets (rabbit chow), and ordinary corn meal that I get from the feed store. It's a lot cheaper than commercially bagged organic fertilizer when you buy 50-pound bags. The application rate is 15 to 20 pounds per 1,000 square feet.