Why would a Public Lake and Dam in Ohio have a sign Warning Keep Away Periodic Posionous Gas ?

 I was recently traveling thru Ohio after stopping to see a friend when I decided to travel the Ohio Byway Route Its a great weekend drive past Farm and field when I came across a sign for Clendenning Dam So I had to check it out  .

But its one of the strangest designs for Man Made  Lakes and Dams I have ever seen to make it even more intriguing where signs warning about Poisonous  Gas ? keep out  So whats the Story

Well this lake built by and maintained by  The Army Corp of Engineers in 1933 out of an old Quarry  to help control flooding in the area  has a most unusual Spillway set up.

https://kayakingacrossohio.blogspot.com/2015/10/clendening-lake-wisteria-wisteria-and.html

First to even get to see the lake and dam you go by the Spillways  exiting point where you see the signs  then have to wind around the mountain they cut thru to make the spillway tunnel  ,

 

Which is where the problem begins instead  this spillway was drilled thru hard rock and since this is Coal Mining area the local coal seams will occasionally leak out  Sulfide into the lake which when it combines with lake water produces Hydrogen Sulfide    which had a very strong rotten egg smell and is very hazardous.. and concentrates around the spillway area

The lake itself which is undeveloped and beautiful  had no such smell when I stopped to look around and take  pictures  but with this years drought there is a warning to Kayakers and Fisherman about strong plume developing. 

https://www.ohiogamefishing.com/threads/clendening-spillway-warning.121573/

 

If you go to visit the lake Cell Service is very limited and there is a small picnic area with playground with Restrooms and Two 1.1 mile trails to hike