Thank you for your plant identification question. From what I can see in your photos, this would not be a S. latifolia, also known as an Arrowhead wapato, because its leaves are not arrow shaped. (I've attached a picture of a positively identified S. latifolia.) Rather, I believe it is a Sagittaria fasciculata, and have attached a photo of it as well. It is endangered and native, but not to the Pacific Northwest, as indicated in this plant profile. Hope this is helpful.