Just below Morony Dam is a well-known hydrologic feature of the Missouri River known as the "Big Eddy."

The large stream creates significant undertow and turbulence, which is not easily seen by boaters approaching from either side of the confluence of the two waterways.

The Lewis and Clark Expedition camped on the west bank of the Missouri River just below the Big Eddy on June 15, 1805, after the hydrologic feature held them back temporarily.

[9] The area is primarily reached by water, but the head of the Big Eddy Land Trail is nearby.

[10] In 2010, a man and his son were jetboating in the area and barely avoided drowning after the Big Eddy sucked their machine underwater.