Mud Lake is located less than a mile from the community of McCook Lake, South Dakota. The lake had once been the main channel of the Missouri River.
In the nineteenth century, before the Army’s dams, pile dikes, and revetments went into the river, the Missouri constantly shifted the direction of its channel. The valley’s soft, sugary alluvium easily melted away when touched by river water. During its April and June rises, the river rapidly eroded its banks, cut-off long bends, and pushed into its former channel areas. When the river abandoned one of its bends – that bend became an oxbow lake – like the one at Mud Lake.
In the twentieth century, the majority of the river’s oxbow lakes filled in with accumulated silt. Valley farmers then converted the former oxbows into fields of corn and soybeans. Despite the efforts of valley farmers, some of the old oxbows are still visible across the valley floor. In western Iowa and southeast South Dakota, notable oxbows exist at Brown’s Lake, McCook Lake, and Mud Lake. The oxbows are signposts of where the Missouri once flowed – and messages written in alluvium in a long-forgotten language. An attentive observer can still read the words and understand their meanings.
The oxbows served a number of ecological and hydrological purposes. For instance, the lakes acted as spawning sites for fish. Perch, bass, bluegill, and northern pike, to name just a few species, moved from the faster, murkier main river into the clearer, calmer oxbows to lay their eggs. The resultant fingerlings found the warm, zoo-plankton-rich waters ideal for rapid growth. The oxbows also acted as natural flood control reservoirs during the river’s annual rises. Water spilled over the Missouri’s banks, cascaded down the sloped valley floor, and entered the oxbows. The oxbows, by holding some of the Missouri’s floodwaters, lowered the height of the river’s flood crests.
When the Army built its upstream dams and its downstream navigation channel, it severed the link between the big river and its oxbow lakes. Fish lost spawning areas, while humanity forfeited a cost-free means of reducing the Missouri’s flood crests.
Long ago, the Missouri cut-off its channel at Mud Lake. Later, the Army’s riprapped banks reinforced that cut-off, preventing any re-connection between the river and the lake.
Today, the Missouri’s floodwaters are approaching its former channel at Mud Lake. This is a concern to the Army Corps of Engineers, the organization charged with managing the Missouri. Army officers fear that if the Missouri does enter Mud Lake it will race through the oxbow, loop to the northwest, and inundate the houses in and around the town of McCook Lake. To prevent that scenario from happening, the Army is now hastily building a levee across the southern end of the lake. But the question on everyone’s mind is whether the levee will be able to withstand the tremendous force the river can bring to bear against it. One official on the scene doesn’t believe so. He’s convinced the river will easily push through the levee and swamp the nearby houses. His doubts about the strength of the levee are shared by others, it’s why the residents of McCook Lake are watching, and nervously waiting, for the Great Missouri Flood of 2011 to challenge the levee at Mud Lake.