Well, I've been trying to get this blankety blank thing to post for quite some time - things have timed out repeatedly... here's what I wrote several hours ago:

Welcome. 200,000 gallons - an unusal unit of measure for a pond <grin> - let's say about 27,000 cubic feet, which would be a bit over ½ acre-foot of water. You don't say how far north you are, but I will assume that an average depth of 5 feet will (barely) let fish winter over or leave you about 1/2 your water available during the wintertime IF you start with a full pond (but not both at the same time). If you're up high or into upstate NY, that depth needs to be increased.

So, say a surface area of about 100 feet by 54 feet with an average depth of 5 feet. An expansive soil - clay - would be the cheapest liner (plus it's self-healing) IF that's the soil type you have - too many variables to cost that are dependant on info you don't supply to swag more than that.

That is a big hole to hack out with a small backhoe - really, with any backhoe - and the buckets on those are for loading, not digging. It's the wrong piece of equipment. A bulldozer is better - much better - at that sort of thing, or PERHAPS an excavator ("power shovel" on crawler tracks). But rural ponds are rarely made by excavation - usually one selects a suitable natural drainage and constructs a dam - with or without terraforming before filling.

In my state (Illinois), a 1/2 acre-foot pond would probably not be regulated, but you need to check your own state laws. Usually it's a fairly simple decision matrix involving amount impounded, height of impoundment, and danger (if any) to downstream developments. Regulation brings required maintenance and inspection and certification by registered professionals on a regular basis - which is actually very good sense.

Hire a professional - a registered professional - to design the pond for you - it will be the cheapest way to wind up with a pond that does what you want. Don't forget to consider mosquito control, specifically of the cuellex type mosquitos, because West Nile Virus is for real (and not the only disease that cuellex is a vector for) and neighbors within a couple of miles would be warranted in complaining if you don't control mosquitos. Larvicides are available, but I personally feel that natural controls are best (consult your state DNR and/or Dept of Public Health for native species that feed on mosquito larvae)

Oh - is your volume estimate of the size pond you want or of the amount of water you want to be able to draw off at a specific time of year? And all ponds eutrify (die by filling in) - very quickly if one does not construct and maintain a forebay to capture sediment that runs in. It will make a huge difference in the size of pond you build...

There's a whole lot more, but once you talk to a professional you'll be on the right track.

You could chat with the folks over at The Mother Earth News about your pond, but they (M.E.N.) have suggested things in the past that are, erm, well, oblivious to impacts/effects on neighbors - which is about where my rights end and my neighbors rights begin... talk to a professional and then decide if you want to hire him/her.

Hope this helps!

PS - I've glanced over the other replies and links and don't disagree with the other posts - but you are talking a decent farm-sized pond in a northerly clime - not a backyard pond. Change your AVERAGE depth to 2 feet and you're now talking about a 13,500 square foot surface area pond - say, 100 feet by 135 feet. Small for farms, but huge for folks who aren't raising fish or livestock.

Regards,

Tom