From Oregon Flora, Gardening with Natives:
Wapato is a handsome emergent plant needing wet habitats. It grows well in full sun or light shade in shallow water, making it ideal for planting along pond and lake margins or ditches and swales. In ideal conditions it spreads vigorously via rhizomes and tubers, producing arrow-shaped basal leaves up to 10 inches in length. Flowering scapes emerge in summer producing three-petaled white blooms with button-like yellow centers. Aside from providing erosion control and water quality improvements, wapato is an important food source for wildlife.