In Texas, Diquat is usually a good option, but use caution because killing too much at one time WILL cause O2 problems. Fluridone is also a good option for smaller shallow ponds and usually don't involve near the risk of O2 depletion beacuse of how slowly it works. Fluridone also has a distinct time window so I would start your research with these two products. And as always make certain that you research and follow all labels, laws and state regulations. Especially being in California!

Grass Carp or Tilapia may provide some help but it's doubtful that they will offer control anytime soon. Especially if a majority of your pond is already covered.