When boating on Lake Texoma, which like its name suggests, is on the border of Texas and Oklahoma, you better heed the warning buoys and stay away from certain parts of the lake. Why, you ask? So you don't get sucked into this giant 8-foot wide whirpool that can swallow a full-size boat!
The whirlpool is an intake vortex that drains the lake, which is one of the largest reserviors in the United States and formed by the buildup of water at Denison Dam on the Red River. When the water level on the lake rises to a certain level, the US Army Corps of Engineers open the floodgates that drain the lake, just like a big bathtub.
http://youtu.be/8p82uGXUUTA?t=22s