The following indentifies several pollution issues affecting the watershed and details possible solutions to reduce pollution on Grand Lake St. Marys.

Nutrient Runoff

Nutrient runoff from livestock waste, fertilizers, and other sources is one of the major reasons for lake degradation.  Rainwaters wash waste and fertilizers from agricultural land into tributaries that ultimately lead to Grand Lake St. Marys, which has loaded the lake with nutrients such as phosphorous and nitrogen. Between 150,000 and 200,000 tons of silt enter the lake annually.

The abundance of phosophorous and nitrogen upset the natural balance of the ecosystem and provide a breeding ground for blue-green algae.  Despite the name, blue-green algae is not a plant but bacteria that gets its energy through photosynthesis (cyanobacteria).

These bacteria produce toxic peptides that harm plants, animals and humans.  Such toxins are harmful to the liver, nervous system, and body organs, and can cause health complications ranging from mild rashes and sneezing to severe gastrointestinal distress and convulsions, respiratory distress and respiratory failure, paralysis, and death.

Agriculture isn't the only source of nutrient pollution in the Wabash Watershed, but it is the main contributor according to the Army Corps Of Engineers: 

Nutrient runoff is facilitated by:

Over-application of manure.  The animals in the GLSM watershed produce 600,000 tons of raw manure each year, which requires 81,000 acres of land area to remain within recommended guideliness.  There are only 48,000 acres of land area available to filter the manure.

Subsurface drainage tiles provide a conduit for nutrients to reach the lake faster.

Spreading manure over ice in winter months means the manure flows to the lake along with the meltwater in the spring.

Using roadside ditches as drains, which act as tributaries to Grand Lake St. Marys.

The fact that the Greater Grand Lake St. Marys Region has some of the highest agricultural activity in the nation.

Industrial and Commercial Drainage

Another source of pollution for Grand Lake St. Marys is industrial and commercial drainage.  Some sources are directly piped into the lake via industrial and residential channels.  Examples include septic tanks, package plants and the lack of community sewage treatment facilities.

Other Pollution Sources

Other pollution sources include residential lawn fertilizers and waterfowl.


The key to saving Grand Lake St. Marys is to prevent pollution from entering the lake and its tributaries.  Fortunately, many of the practices that prevent pollution also make for more efficient agricultural and community operations, ultimately saving time and money and making business more profitable. 

Winter crop cover

Best practice manure management (following guidelines in 590 and 633)

Erosion control fencing

Septic system pumping

Community sewage treatment facility installation

Septic inspections and certifications every two years

Proper lawn fertilizer application

Filter strips

No-till farming operations with conservation buffers

Comprehensive livestock nutrient management

Looks like the problem and the cause are identified. The logical solution would be to stop the majority of the "loaders" at their expense. What is so difficult about this solution? I know if the average homeowner would throw their refuse in Grand Lake it would not take years of debate and hundreds of thousands of dollars to figure out what to do. They would be cited and fined.

Submitted by Anonymous on Mon, 06/28/2010 - 8:11pm.

To put it bluntly - agriculture is killing Grank Lake St. Marys. Unless new pratices are put in place very soon the future looks dire.

Submitted by Anonymous on Mon, 07/05/2010 - 8:32pm.

It is obvious to those with tunnel vision. To say that agriculture is killing Grand Lake is a "you done it" attitude that will benefit no one!

Agricultural practices have advanced so much over the years, and the landowners are using best mangement practices. Lest we forget the amount of development on the south side of the lake alone, that destroyed how many hundreds....maybe even thousands of acres of natural wetlands that stopped sediment and nutrients from entering the lake. Houses and development that are occupied by the very people who complain about the quality of the lake water. Are these people to blame? Not directly, maybe if they over fertilize their plush lawns. How about the farmer? Maybe by inheritance, and if they make no efforts to do the right thing How about the fact that the lake was never intended to be a recreational lake?

This was a lake dug by mostly Irish and Chinese immigrants to supply water to the Miami-Erie Canal. It was dug deep enough to accomplish this goal...and it did. Now, had they known that nearly 200 years later this body of water would have probably designed it completely different.

I think we all forget that this area was a swamp, and it wants to be a swamp. Does that make you happy? No, and me either. I enjoy the lake, just like everyone else does. But, I am getting sick and tired of everyone looking to the men and women who raise the food on your table, and everyone blaming them for the lake problems, all while you cook the burgers and brats on your patio, made from the animals they produced. So, unless you are raising your own fruits, vegetables, grains and meats, and you're not going to Wal-Mart, Cheif's, Kroger or any other grocery store, lets not attack the agriculture in Mercer, Auglaize or Darke counties.

Am I a I am not. Do I have all of the answers...absolutely not. Do I want the lake to improve...absolutely! We need to work together folks! Farmers, lake enthusiasts,citizens, legislators, SWCD's, State Parks...EVERYONE has a hand in solving this problem. If a group is going to go off and do their own thing...the job as a whole will not get accomplished. WE HAVE TO WORK TOGETHER!

Submitted by Anonymous on Wed, 07/07/2010 - 12:27pm.

I couldn't agree more you lets just work on fixing the problem. The lake is a beautiful spot

Submitted by Don (not verified) on Mon, 09/29/2014 - 1:27pm.

The prime problem appears to be spreading too much manure on fields that are extensively tiled. Any significant rain results in direct drainage of soluble phosphate through the fields and into the drain of the watershed (and completely bypassing the riparian buffer strips).

There is no way that you would consider dumping raw human sewage on the land but this is what is done with animal waste. One cow equals 7 humans for waste and I don't know the hog equivalent but it is probably at least 2 to 1. 10,000 hogs create the waste equivalent of a city of 20,000. For a city, a sophisticated sewage treatment system is required and the phosphate release for the system is controlled. Why not the same for any animal operation of any size.

Try prohibiting field application of manure for two years and track watershed quality. See if this solves the problem. If it does the farms should be required to build cooperative sewage treatment facilities so that the lake is protected.

Submitted by Bill (not verified) on Thu, 07/08/2010 - 10:02pm.

Why is only 48,000 acres available to spread manure? Mercer County is 296512 acres. 75.86% cropland and 9.1% pasture = 251916.6 acres to spread manure.

Why was all that money spent on mixing instead of the simply drawing the phosphate rich water off the bottom by fixing the bottom draw at the dam. The lake is far too shallow to make aeration/mixing practical...common sense for lake managers.

I posted about the alum as a temporary fix a year before they figured that one out. Only works if you treat the entire surface or inject the incoming water. Total waste to treat a small percentage. Injection of alum at major water sources seems to make more sense than trying to drive a boat back and forth and covering the entire lake.

BTW lawn fertilizer contains up to 24 times the amount of P, laundry detergent 5 times, dish detergent 7 times as compared to manure. I'm assuming all those complaining have stopped using the above products. These items alone, even if only a small percentage of the overall problem, could be giving the blue-green algae the edge over less problematic species.

Submitted by Anonymous (not verified) on Mon, 01/17/2011 - 6:07pm.

Just wondering, when was this study done, that the Army Corps of Engineers did?

Submitted by Anonymous (not verified) on Mon, 12/13/2010 - 6:01pm.

Everyone can rag on the agricultural industry, but the fact remains that Grand Lake was never meant for recreational use it was meant as a storage of excess manure. Also agricultural brings in more profit than the lake ever would.

Submitted by Anonymous (not verified) on Mon, 04/11/2011 - 8:33pm.

When was this Grand lake created ?The comments seem to have two opinions as to the reason it was created .We are trying to clean up a small chain of lakes in central Alberta Canada and need help .

Submitted by Friends of Chain Lake (not verified) on Thu, 02/20/2014 - 2:55pm.

Friends of Chain Lake, please take a moment to check out the LIA Education Series. The first part covers the history of Grand Lake St. Marys, where you'll learn that it was originally constructed as a reservoir for the Miami - Erie Canal. 

Here's the link:

Submitted by brian on Thu, 02/20/2014 - 3:59pm.

I find it hard to believe that Grand Lake St.Mary's...the largest inland lake in Ohio was designed for the farmers to dump manure. Figure this out! No body of water should be designated as a dumping ground...

Submitted by Anonymous (not verified) on Sat, 07/11/2015 - 9:11am.