Yellow Pond Lily, a native species, has been added to the USWildflowers database (08/12/2010.)  Scientific name is Nuphar lutea.  This plant also is known by the common names Cowlily, and Spatterdock.  Photo below was taken on the Stuart River in the Boundary Waters Canoe Area Wilderness in MN on  08/02/2002.

Yellow Pond Lily - Nuphar lutea