Here is what the guy from the Soil and water district just emailed me:
We were hoping to go bigger but that may not be the answer according to him:

I measured your pond at about 3/4 of an acre the drainage area I measured at about 6 acres normally you would want at least a 10:1 ratio in central Illinois. So I wouldn't encourage to expand the area of the pond very much if any. Fish need an area at least 8 feet deep over about 1/4 of the surface acreage of the pond. Cleaning out these ponds can get pretty expensive so if your goal is to be able to maintain fish use the this equation to figure how much excavation you would actually need.