Essay: Oxbow Lakes

One of the signature characteristics of coastal rivers throughout the South is their winding, sinuous channels and the many oxbow lakes formed as a result of these twisted channels. Oxbow lakes get their name because their shape resembles the “U” of the old wooden oxen yoke. They are formed during big flood events when swift, raging waters take a short cut directly across the neck of a river meander (curve) and carve out a new, straightened river channel. Over time the river channels that formed the meander (now called the inlet and outlet) fill in, the old meander is cut off completely from the flowing waters of the main channel, and it turns into the calm, placid waters of a lake.

There are several oxbow lakes in Congaree National Park: Weston Lake, Dead River (a rather poetic term often used in oxbow lake nomenclature), Horseshoe Lake (another common name associated with oxbows), Devil’s Elbow, and Bates Old River. Most oxbows are only a few acres in extent but Bates Old River, one the largest oxbow lakes in South Carolina, is four miles long, counting the inlet and outlet, which still open to the Congaree River. Oxbow lakes are subject to sedimentation and not very deep, running about five to eight feet. During the fifty-year drought of 2007-2008 I saw Old Dead River, Cooks Lake, and Horseshoe Lake “bone dry.”

Horseshoe Lake on the lower Wateree completely dried up during the big drought of 2007-2008

Perhaps the most interesting of Congaree oxbows is Weston Lake, known to many park visitors who enjoy its still waters and scenic beauty from the high boardwalk overlook. Unlike most oxbows that are close to the river and of fairly recent origin, Weston Lake is two-and-a-half miles north of the river, suggesting a lake of much older origin. In fact, David Shelley reports the age of Weston Lake, based on carbon dating of sediment cores, to be 2,890 years old! Another interesting feature of Weston Lake is that local lore claims it to be bottomless. In 2009, investigators from the University of South Carolina conducted a study of the five-acre lake and found it to be unusual in many respects. Much of the steep-sided lake was more than twenty feet deep, with the deepest point being almost twenty-five feet. This is incredibly deep for an oxbow lake in a South Carolina floodplain. The researchers also found the bottom of the lake consisted of gravel rather than mud and organic matter. The depth and gravel bottom told the researchers that for some inexplicable reason, Weston Lake was not filling in, which is what lakes are supposed to do. One possible explanation they came up to account for this is the presence of artesian wells on the lake bottom which keep sediment and debris from settling.

A view of Weston Lake from the air

Most oxbow lakes have a short geological life span. Devil’s Elbow was formerly a sharp bend in the lower Congaree River until an oxbow was created out of it in the 20^th century. In the 1970s I could drive a johnboat from the river into the lake but over the past forty years the access channel to the lake has filled in.

Old plats and maps from the 1700s clearly show that many Congaree oxbows were then part of the main river channel but over the past 250-300 years have turned into lakes with virtually no access to the river except during big floods. And some oxbow lakes are not even lakes anymore.

“Big Lake,” a tupelo-filled depression located in the center of the park just below Running Gut and a little west of Dead River, was labeled as such on a 1943 Hopkins topographic map. A 1972 topographic map, however, shows Big Lake as low swamp forest rather than as a lake. The only time it now holds water is during floods. Since major flood events create oxbow lakes, and many such floods have been reduced with the construction of upstream dams, inquiring minds may wish to ask “are oxbow lakes a thing of the past?” “Is coastal river geology now frozen in time?” Although the process may have been slowed down, I have seen within the past ten years a new oxbow lake being created within park boundaries. A 2000 aerial photo shows a small channel of water cutting across a narrow neck of high ground on a Wateree River meander a little south of Two Rivers Farm (there was no channel according to 1994 photography). By 2006, this small channel had been expanded enough by swift floodwaters that it was now the main channel of the Wateree – and a new oxbow lake which I dubbed “New Lake” was created in the process. Interestingly, by 2018 the eastern side of the newly created lake had already started filling in!

Congaree’s old river channels and lakes tell a fascinating story of the past and reiterate the old saw that the floodplain belongs to the river and the river belongs to the floodplain. We can only speculate where the channel will be thousands of years from now but it’s probably safe to say it won’t be in its current location.