john barsell wrote:

I propose to build a stock watering pond in an existing drainage channel.
(California) Are any Federal permits required and if so by which agency?

John,

Your best bet would be to check with what we here in Texas call your
"county agent"; they're associated with the state land grant college.
Usually those guys can tell you just about everything you need to know.

http://ucanr.org/ce.cfm

Dale