The answer to 'why is my gutter moldy' is that gutters can become moldy due to a buildup of debris, moisture, and lack of proper drainage. Mold thrives in damp, dark environments like clogged gutters that aren't regularly cleaned.
Some common causes of moldy gutters include leaves, twigs, and other organic matter accumulating over time, as well as poor gutter installation or damage that prevents proper water flow. Symptoms of mold in gutters include a musty odor, visible black or green growth, and water pooling in the gutters.