Northwest Ohio Tourism
Support our advertisers

Grand Lake St. Marys

Grand Lake St. Marys

It is 9 miles long and 3 miles wide and is the largest man-made lake in Ohio. Grand Lake St. Marys covers approximately 13,500 acres,is fed by eight streams and straddles 2 counties (Auglaize and Mercer). Grand Lake covers almost 3 times as much ground as all of Ohio's natural lakes combined (excluding Lake Erie).

The shallow lake was originally constructed all by manual labor as a feeder lake for the Miami-Erie Canal. At one time, it was the largest man-made lake in the world and it still remains the largest lake in the world constructed entirely by manual labor. It's official name is just Grand Lake, but state locals always add the St. Marys. St. Marys is a small town on the east end of the lake.

Today Grand Lake serves as the drinking water supply for the City of Celina located on the northwest corner of the massive body of water. The lake is also highly prized for its recreational value for unlimited horsepower boating and the Celina Governor's Cup Regatta held here each year.

Environmental Concerns

Grand Lake has had its share of environmental problems over the years. At one time oil was discovered nearby and some enterprising individuals decided that there was probably oil underneath the surface and they developed a way of creating platforms from which to drill for oil, making it the first location to use platform drilling over water. At the hey day of the oil drilling, Grand Lake had many oil rigs drilling and extracting the black gold found deep beneath the surface.

Since Grand Lake is fed by several small streams that run through large agricultural areas consisting of some 450 farms (of which 300 have livestock or poultry), super-saturated phosphate run-off has become an increasingly problematic development for the area. Livestock agriculture including cattle, hogs/pigs, and poultry has increased dramatically in the primary watershed of Grand Lake over the last 10 years. Efforts to control runoff from these farms has not increased to any great extent, but this attitude is beginning to change.

Chemical decontaminates are being tested at the lake, but this is only a temporary fix. Reduction of the phosphates coming from the increasing number of livestock farms must be addressed. This may involve removal of animal waste for processing elsewhere. It may also involve limited the number of animals allowed on any farm. However, the ideal situation would be to re-establish important wetlands that will naturally filter water before it moves further downstream and into the lake. Additional education of the owners of all agricultural concerns that influence the lake's watershed also needs to be enhanced.

St. Mary's Canal

Miami & Erie Canal

It took some 9 years to excavate the large reservoir by more than 1,700 men earning 30 cents a day. Construction began in 1837. In 1845 the man-made lake covered 17,500 acres and was 7' deep. The reservoir was used t

Grand Lake Oil Platforms

Oil Wells of Grand Lake

At the peak of the oil boom in western Ohio, there were more than 100 wells on the reservoir and hundreds more around the eastern shore. By 1913, the boom was over and more productive oil deposits had been discovered made the Grand Lake operations too expensive to continue.