Water molds belong to the group known as oomycetes. The water molds resemble other fungi because they have branched filaments and form spores. However, the water molds have cellulose in their cell walls, while other fungi have chitin.
Oomycetes have a complex reproductive cycle which includes flagella‐bearing zoospores. Certain water molds are parasites of fish. Others cause disease in plants such as tobacco, grapes, and potatoes.