I also agree draining is your best bet, but I don't think you'd have to wait a year before digging. If we did that up here no ponds would ever get done. I just did 1 of mine drained it and dug it down to 6' in less then 2 weeks. It does take some know how to work the dirt so that you can get in and dig out the muck, but once you get a start stick with it{very boring}. I am in the process of cleaning up another 1 only needed to drain it about half way, cutting banks back. We have gotten rain allmost every single day of this summer so if I wait for it to dry up I'd never get it done. I'm not knocking letting it dry if you have the time and the right weather, but up here it is not an option. Another thing that may help you is to either rent an excavator{fun to operate, just be safe} or find a friend that has 1. Nothing beats an excavator for pond digging except a good operater on an excavator. But even a guy with some common sense and safe operating skills will do a fine job.
Find a pump/hoses sometimes cheaper to buy then rent????
figure out what type of machinery you can get a hold of???
figure out if you'll have help, can help to have 2 operators one on a ex/BH and one on a tractor dozer etc to move dirt away.
MOST IMPORTANT !!! figure out what you'll be doing with the dirt, hardest part of pond work.
Last but not least time!!
keep us updated on your progess.