Welcome Jess, I don't believe anyone that lives in Washington State says ya'll......

I would start (before you buy any property) by hitting some of the counties NRCS offices where you are looking at property and talk to them about the ins and outs of building a pond, or buying a property with one already on it.
Reason for saying that, is I don't know what it costs to build a pond there, nor what (if any) permitting process is required. You may be money ahead getting one already built.
Ask them if you wanted to renovate it, what permitting process would be needed too.