Mushrooms!

Mushrooms and toadstools are actually a good sign--they indicate a high level of soil fertility and point to a long future of healthy grass growing in good, moist soil. The mushrooms and toadstools appear when a certain set of rather poorly understood climatic conditions occur. As soon as those conditions change, the mushrooms will disappear. Though they are unsightly, they pose no threat to your lawn. Treat them like a trophy--they mean that whoever prepared your soil prior to planting did it right, and they mean that whoever manages your turf is doing that right, too.