Let’s assume you have a perfect site, IE valley with a narrow opening, lays properly, and good clay for the dam. If that is the case I’d say it is ‘doable’ by one man, an excavator, dozer, and either a scraper or dump truck, given enough time. If you are talking excavating it out of a flat field, I’d say no that is not doable for any reasonable amount of time and money. First example your talking about moving tens of thousands of yards, second example hundreds of thousands of yards.
We haven’t even gotten to the permiting part. Again, an ideal scenario is you keep the dam under 26’ tall, there are no wetlands involved, no stream impoundment, watershed area is sufficient but under 1000ac, and you live in a state that views pond construction favorably you might get off somewhat easy. The Army Corps of Engineers is undoubtedly going to be interested in what you are doing. Change any of the aforementioned conditions and you’re also going to be dealing with a slew of state and federal three letter agencies. Figure on at least a year to get all the legal stuff taken care of.