Aquatic perennial. Grows 3 to 4 feet tall. Leaves are long, flattened, sword-like and 3-4 feet tall. Yellow flowers are produced on erect plant stalks with multiple flowers per stalk. Fruit capsules are large, 3-angled and up to 4 inches in length with disk-like seeds. Large plant clumps are formed from lateral growth of rhizomes. An infestation of yellow flag iris demonstrates a dual impact on both human interests and native environments. This plant displaces native plants including sedges and rushes. This can reduce the carrying-capacity of wetlands for waterfowl and disrupt other ecological relationships. Flow in waterways including irrigation canals and flood control ditches can be severely restricted. Removal is expensive, and control of heavily infested areas can be cost-prohibitive. Once established, it is an aggressive invader in wet habitats. It invades riparian, open water features and irrigation ditches. No bio controls available at this time.