I might stay with Kirk Strawn hybrids. Most, if not all, were developed in College Station so they should do fine in LA. I know purchasing hybrid lilies is obviously more expensive than finding some in another pond, but 5-6 years from now you'll be glad you stayed with a known plant.
My experience has been that Colorado's spread a little faster than the Denver's, but I can't remember ever seeing them in more than 4' of water. The Colorado's are extremely hardy, and have survived multiple droughts and did fine.
Here's list of his hybrids, but I'm not sure which one's are still available.
http://www.victoria-adventure.org/more_than_links_images/kirk_strawn/strawn_waterlily_cultivars.htm This pic of some Colorado's than I planted in marginal water years ago. They spread laterally along the bank, and stop spreading once they hit the deeper water. This was an afternoon pic, so the flowers had already started closing.
EDIT: Just an afterthought, but hybrid lilies scream throw a frog at me, so I do.