IL may be different than IN, but in IN, you'd be screwed. I actually sold my house, property and moved. I owned nearly all of a 3 acre lake but had a half dozen other morons that had property that touched the "natural" waterline.
Problem. All expenses for upkeep and maintenance was divided up according to what percentage of the lake was owned. Therefore, I bore nearly 100% of the costs. The IN DNR and conservation services told me that since their property went into the natural water level, they had rights to the entire lake.
Bigger problem. I built a dock in the lake on my property. The other bumbling morons and their offspring proceeded to use my dock as their own. Not only did they use it, but they left their trash and soda and beer cans on my property.
I sought legal council because since I owned a full 100% of the dam, I decided that I just wanted to use that dirt elsewhere and would just drain the stinking lake!! IN law forbid me to do that since I would "devalue" their property.
My only justice I got was when I called the health department of that county and told them that 4 of the surrounding houses had their septic systems draining into my lake. They did a dye test and all 4 houses proved to have some sort of leakage into the lake. They were each given 14 days to correct the problem or evacuate their homes until the problem was fixed and inspected by the health department. Oh yeah, the neighbors loved me for that!! /forums/images/graemlins/grin.gif
I even had some people who purchased property across the road from my lake that had written into their deed that they had "lake rights". Only those people got shot down by the law. Since that was not in my deed and I owned the lake, whoever wrote their deed had no right at all to grant "lake rights" to my property.
Oh, it was really nasty. I had to pay an attorney to get me out of an aggravated battery charge over one incident with one of the neighbors. You can use your imagination as to what happened there. It was worth the expense!!!!
The bottom line in IN seems to be that if you have property that touches the natural waterline of a body of water, you have rights to use the entire body of water. After all the problems and expenses I had, it wasn't worth it. I now have a nice lake where I live now. Needless to say, it is completely confined within the borders of my property!! Good luck! I know only too well where you are coming from.