If you are 100% positive that it's lake water, then the sources could be... drain plug, transom assemblies, bellows, thru-hull fittings such as transducer or seacocks. Of course, this is barring any type of hole in the hull, which would likely be obvious.
The way to figure it out is no different for this boat than any other boat... start with a completely dry bilge and observe closely. Paper towels in key areas, for example, can help.
Paul, it is not normal to have water in your bilge. In some cases it's a "no big deal" thing, but in other cases it could be a bigger problem that's just starting. There's LOT'S of threads about determining whether the source is raw water, rain water or even a boat system that's leaking. Do a search for those - lot's lot's of info already out there. Heck, there might even be info somewhere in this thread.
Thanks Dennis, the boat is new to me, and I plan to eventually keep a dry bilge, just need to work the process. I appreciate your thoughts and feedback and will keep the thread posted with what I find. Going to get it dry tonight and put paper towels under the transom assemblies and at the drain plug to see if I can find a correlation.
John