Bass: Others have provided some great advice. My small contribution is that I also live in Illinois and work with the EPA occasionally (I have the regional office number memorized if that means anything) through my work. Not to discourage that route, but I'm not sure that would be very effective in Illinois right now for multiple reasons. First, IEPA seems focused more on fines related to the aftermath vs prevention. Second, I'm not sure how quickly IEPA would jump in on a situation between two property owners like this with no obvious public interest (as in public land, waterways, roads). Third, practically all of the state's agencies are really shorthanded right now. Many of the more knowledgeable staff jumped at the early retirement opportunity a while back. Many of those who didn't wish they did. Frankly, the state's agencies are at the worst I've ever seen. I could post my perceived reasons for this, but probably shouldn't.
I have talked with two law professors at the University of Illinois in Champaign. It is bugging me that I can't remember their names right now, but they were helpful. They also have some good information on the internet. I would search for information related to University of Illinois and property rights.
I would also double check your and his deeds. Your local county clerk's office should have them. I would document like crazy, probably even have someone video tape the pond, and all that.
I would talk with an attorney.
I would try to win him over if possible.
I would explore the possibility of buying his property if you are financially able. If he wouldn't sell to you, explore having a ghost buyer make the transaction (someone else buys it and then sells to you).
Finally, I would hope that the wind blows the fish his way as Russ pointed out. The IDNR poisoned fish in a small private lake surrounded by campers a while back. My office was flooded with complaint calls wanting us to do something about them (fish, property owners, IDNR, and horrible odor). Based upon that situation, it might be safe to say that he won't do that twice if the wind is blowing his way. ;\)
Jeff

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