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EUREKA, Mo. (KTVI) — A sinkhole drained a 50-year-old man-made lake Sunday night.

The 17-acre man-made lake’s clay and limestone bottom appears to be forming cracks. The St. Louis County Parks Department is concerned since the lake is the primary source of water for the herds of bison and elk in the area.

The lake, located in Lone Elk Park, also formed a sinkhole in 2016, but the one formed Sunday night is worse.

At the time of the 2016 sinkhole, St. Louis County Parks Operations Manager Jim Gerken said rock creates a lot of sinkholes, streams and caves, so when you build a lake on top of that material, it is not uncommon that a hole could develop.

On Friday, St. Louis County posted on its website that the lake was “leaking.”

“The lake at Lone Elk is leaking. The Parks Department is aware and will assess the situation once the water level stabilizes. Road and trail access is not impacted and the park remains open,” the county stated.