I recently bought a property in rural Richmond (Marlborough forest area) and there is a fairly large pond in my backyard that I would like to somehow make more appealing. It is about 80 feet by 40 feet in size and it currently has alot of 'weeds'. I am new to gardening so I don't even know where to start. Is there a product that I can use to clean out the weeds that are there now? Although, there are some really pretty yellow irises that I don't want to get rid of. There are also some fish in the pond that I guess the previous owner put in (catfish, perch, some minnows) that I don't want to kill and numerous birds (ducks, herons, bitterns etc..) that frequent the pond that I don't want to get rid of either. What can I put in the pond to make it less 'murky'? Sand?
Any help or advice would be appreciated. Thanks!

There really is no miracle additive for a pond that large. Over time, you need to develop an ecosystem which includes a mix of plants as well as some sort of recirculation to keep the water moving, at least a little. With a pond that large, it will be rather difficult, I think. Also, some fish make the pond very murky by digging through the dirt on the bottom of the pond.

I would start this year by adding some plants like Water Lilies, Rushes, Marestail, Arrowhead, etc. Pick hardy plants so they can multiply and start making an ecosystem. There's nothing really to get "weeds" out of a pond that I would suggest so it will be a matter of manual control ripping out the ones you don't want or just learning how to integrate them into the landscape.

I hope that helps a little. With a pond that size, it will take quite a bit of research and trial-and-error to get it the way you want it.

Take a look over at http://www.aquascapedesigns.com/. They do ponds and also have a message board that may help.

Good Luck!