During the spring or summer a circle or arc of stimulated grass or toadstools may appear in lawns. These are turf abnormalities called fairy rings. The rings can be up to 20 meters in diameter, but most are between 1/2 meter and 5 meters across. A fungus that plagues many courses and lawns, fairy ring is caused by mushroom fungi that live in the soil and thatch layer. Early symptoms include circular rings of overly green grass. The fungus has three types: Type I rings include a center section of dead grass surrounded by a ring of dark green grass; Type II rings do not have dead grass - only a band of dark green turf, sometimes with mushrooms; Type III rings have only a ring of mushrooms without affecting the grass color. Fairy rings usually do not present a lethal threat to a lawn or other turf, but sometimes a ring of dead grass occurs in addition to the ring of stimulated grass growth. Fairy rings normally recur each year, and their diameter slowly increases.