Nuphar polysepala

Nuphar polysepala, also known as the great yellow pond-lily, wokas, or wocus, is a perennial, rhizomatous, aquatic herb in the genus Nuphar native to western North America. It is commonly found in shallow muddy ponds from northern Alaska and Yukon southward to central California and northern New Mexico, and can be recognized easily by its large floating leaves and bright yellow blossoms....read more on Wikipedia.