These reports are available on the internet at Indiana State Department Of Health , search for the keyword 'mercury'. The detailed studies are no longer on the internet but are available by mail from the Indiana Department of Health. You can read the synopsis on the searched page.
Some mercury reaches Indiana waters occurs naturally.
Besides, the same soil, relatively, and the same wind blows over every state that surrounds Indiana. The mercury levels in the fish in every body of water, other than those with identified sources of mercury, are what the scientists consider to be 'back ground' readings. Referring to the IDEM report, you find another interesting fact. There you have it. Patoka Lake is the cleanest lake in the State of Indiana.