I had posted this earlier as the Second largest hole in a lake. However as per the latest information received by me it is Fourth largest. I have therefore merged this post in a combined post which now includes all the large "Hole in A Lake"
The strange looking hole in the lake is actually an uncontrolled type of spillway to control the level of the Lake created by a dam. Such holes are called morning glory, plughole, glory hole, or bell-mouth spillways.
This spillway located in lake Berryessa , Monticello Dam, California is Fourth largest glory hole in the World.
Image from Panoramio is by Auggee
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