Why do mushrooms grow as freakish "water-rust spot mushrooms"?

If the mushroom house and the surface of the growing medium are not ventilated promptly after watering, the humidity in the mushroom house becomes too high, small water droplets form on the mushroom surfaces, and over time rust-colored spots appear.

Prevention measures: after each watering, open the doors and windows for 30 to 60 minutes to ventilate.