Russ how are you going to lower the water. It seems to me you will (may) have two major stressors , crowding and water quality. If you lower the water 4 feet and evaporation takes another 18 inches that is a high % of your water missing. I used 18 inches as an example that is not thought about often but Ed numerically pointed out in another thread and I discussed in a siphon drawdown thread. As the water goes down the basin from which it comes shrinks and you get exponentially less water and it comes out faster. Further in some cases (most) if you take the water off the to 3 feet that leaves bottom water that is not fertile or oxygenated unless you are aerating. If you have been aerating that may make up for the water quality questions. Bob also posted out the fact that as water evaporates the remaining water has a higher concentration of metals and other bad stuff. As a % that could be a factor even if aerating. Most drawdown as a management tool info I have seen suggests no more than 20% of the bottom exposed which I guess in an avg, pond may be 30% of the water. Unless your pond is a cube you may be close to 60% of your water or more.

Do you have a place to move some fish to so you can bring them back ?

Take a look at Bill's archive on Fish Kills as it has links on stressors and crowding.

http://www.pondboss.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=22;t=000038

Most of the crowding info is wrt aquaculture methods (high fish densities). How old is the pond (fish been in it )? As a general guide most ponds will reach carrying capacity in 2-3 years after fish introduction. Even at normal pond fish capacity (no or only supp. feeding) you will not be at aquaculture operation densities. If you can avoid DO/water quality problems you should have some fish left even with a several mth. drawdown. Depending on which other problem , if any, arise you may be able to treat the problem .