Many people associate Harsha Lake at East Fork State Park in Clermont County with boating and recreation. While those activities are important, that's not the reason it was built.
Harsha Lake's one primary goal: control the amount of water flowing into the Ohio River and eventually the Mississippi River.
Samantha Bachelder is a park ranger with the U-S Army Corps of Engineers, which operates the lake about four miles south of Batavia on the East Fork of the Little Miami River.
"We were originally built because of the 1937 floods that happened in Cincinnati and Dayton," Bachelder said.
Those floods caused major damage throughout the Ohio River valley. The Ohio crested at 80 feet in Cincinnati on January 26, 1937, its highest level ever in the city.
"Congress at the time decided to pass another flood control act in 1938 and basically provided all of us the funding to be able to build these projects," Bachelder said. "Even though they didn't get built till much later on, the funding and authorization was provided then."
Construction on Harsha Lake started in 1970, and it was fully operational in 1978.
It's part of a series of lakes, locks and dams along the Ohio River from Pennsylvania to Illinois designed for flood control.
There are four other lakes for flood control in southwest Ohio and southeast Indiana that are part of the Miami River flood control project. Those include: Caesar Creek Lake in Waynesville; West Fork of Mill Creek Lake in Winton Woods; C.J. Brown Dam & Reservoir in Springfield; and Brookville Lake in Indiana.
Bachelder said Ohio has basically no natural lakes, they are almost all man-made whether they were built for flood control or as reservoirs.
As of Thursday, the Harsha Lake level was about 762 feet above sea level. That's about 30 feet higher than the summer.
Beaches, boat ramps and some buildings are closed because of high water.
The highest the lake can go is 795 feet, but it's never been close to that. The historic high was 777 feet in 2011.
When it comes time to start releasing water, attention will turn to the large, concrete control tower that rises out of the lake near the earthen dam.
"There are hydraulic gates that are in that tower," Bachelder said. "That tower goes all the way down to the bottom of the lake and those gates, we have a couple different kinds. We have our main gates which are very large, and then we have our bypass gates which are much smaller and let out much less water."
Harsha Lake is part of the Corps of Engineers headquarters in Louisville, and Bachelder said officials there will determine how much water to release and when.
"Depending on how much water Louisville says that we can let out, we'll determine what size gate we need to use," Bachelder said. "What they do is they give us a measurement in cubic feet per second, that's how we measure how much water is coming out of the dam."
The release will be controlled and it will take some time for the lake to return to its normal level.
"Each lake is designed to only let out so much water a day, typically they measure that in feet, so you’re only allowed to go down let's say two feet a day," Bachelder said. "That's because we want to prevent erosion downstream and also you can't overwhelm your downstream water because if we all let water out at the same time, you're just going to bring that Ohio right back up."
In July 2010, the Corps of Engineers estimated Harsha Lake had prevented more than $87 million in flood damages.