Originally published by Adam Voiland and Michala Garrison in NASA Earth Observatory, August 28, 2026. Licence status: public domain (NASA’s media guidelines say NASA content is generally not subject to copyright in the United States; “NASA Earth Observatory image by Michala Garrison, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland”). Reproduced here with attribution. NASA and the U.S. Geological Survey are not contributors to TeaLamp and do not endorse it or its use of their work. This story about Congaree National Park shows how a river builds a forest. Changes: formatting, the page’s related-story and download boxes removed, the closing National Park Week sentence left out, two AI-generated illustrations and a short “Key takeaways” section added by TeaLamp. Prepared for TeaLamp by the TeaLamp Editorial Team with the help of AI.
Among the 63 U.S. national parks, few are as defined by a single river’s floodplain as Congaree National Park in South Carolina. While the features are also prominent in other parks, a full 80 percent of Congaree National Park lies within the Congaree River floodplain.
It’s a place home to one of the largest intact tracts of old-growth bottomland hardwood forests in the United States. In this image captured by the OLI (Operational Land Imager) on Landsat 9, the river winds through the forested plain, along with curving bands of green that trace old channels, ridges, and swales left behind as the river gradually migrated across it. Slight differences in elevation in these paleochannels and other landforms affect how frequently they flood, producing distinct ecosystems that appear in contrasting shades of green.
The river flows through flat, soft terrain, which encourages the formation of bends and meanders. Water typically flows faster on the outside of bends, leading to more rapid erosion as the channel carves into the outer riverbank. It moves more slowly on the inside of bends, resulting in the deposition of sediment and the growth of sandy features called point bars. Over time, this process can cut off a bend from the main river channel, forming U-shaped oxbow lakes.
NASA Earth Observatory image by Michala Garrison, using Landsat data from the U.S. Geological Survey, acquired August 18, 2025.
The National Park Service lists Weston Lake, 1.2 miles (1.9 kilometers) from the visitor center, as one of the park’s most permanent oxbow lakes, noting that it is relatively deep and lacks the shallow clay and silt layer found in most of the park’s other oxbow lakes, such as Devil’s Elbow. On the right side of the image is Bates Old River, a roughly 4-mile-long abandoned channel of the Congaree River and one of the longest oxbow lakes in South Carolina. Over time, abandoned channels and oxbow lakes can fill with sediment and become shallow wetlands. Some of these low-lying, water-filled features are known as sloughs, where flood-tolerant cypress-tupelo forests tend to grow.
While loggers targeted forests along the Congaree in the 1880s, challenges such as frequent flooding, interminably muddy roads, and mosquito-plagued conditions meant that most of the floodplain forests escaped the widespread logging that transformed other parts of the Southeast. By the 1950s, conservationists had begun to recognize how rare old-growth forests of this type had become in the region. Congress designated the area a national monument in 1976, and it became a national park in 2003.
Regular floods feed the forest with nutrient-rich silt. Image generated by AI.
As the river snakes its way through the park’s mostly flat terrain, it overflows its banks several times per year, usually in the winter and early spring but also in the summer and fall after hurricanes and major rainstorms. These floods distribute broad layers of nutrient-rich silt throughout the floodplain, nourishing the forests and contributing to the high concentration of unusually large trees in the park.
Wetland forests grow where water and land meet. Image generated by AI.
Over the decades, Congaree National Park has harbored a remarkable array of giant “champion” trees that have held national and state size records for their species. Though individual trees have gained and lost champion status as they have been damaged, have died, or been surpassed by newly measured trees elsewhere, Congaree trees such as the possumhaw (Ilex decidua), water hickory (Carya aquatica), loblolly pine (Pinus taeda), laurel oak (Quercus laurifolia), swamp tupelo (Nyssa biflora), and sweetgum (Liquidambar styraciflua) have held records at times.
Why it matters
Congaree protects one of the last great expanses of old-growth bottomland hardwood forest in the United States — an ecosystem that once covered vast areas of the Southeast and now survives only in fragments. These floodplain forests are biodiversity hotspots: the park holds some of the tallest canopies of any temperate deciduous forest, and its wetlands filter water, store carbon, and absorb floodwaters that would otherwise rush downstream. As extreme rainfall becomes more common, the Congaree floodplain is a living demonstration of how a river, left to flood, builds and sustains the forest around it.
Frequently asked questions
What is a bottomland hardwood forest?
It is a forest that grows on the low, flat floodplain beside a river. The “bottomland” floods regularly, and the hardwood trees — oaks, gums, hickories — tolerate months of standing water each year.
What is an oxbow lake?
When a meandering river erodes the outer bank of a bend and deposits sediment on the inner bank, the bend can eventually be cut off from the main channel, leaving a U-shaped lake. Over time these lakes fill with sediment and become wetlands.
What are champion trees?
“Champion” is the title given to the largest known tree of its species, tracked by national and state registers. Congaree trees have held records for species including loblolly pine, sweetgum, and swamp tupelo.
Key takeaways on Congaree National Park
- About 80 percent of Congaree National Park lies in the Congaree River floodplain, which holds one of the largest intact tracts of old-growth bottomland hardwood forest in the United States.
- As the river meanders, it can cut off bends to form oxbow lakes, which may later fill with sediment and become wetlands.
- Most of the forest escaped widespread logging; the area became a national monument in 1976 and a national park in 2003.
- Floods several times a year spread nutrient-rich silt that nourishes the forest and its record-size “champion” trees.
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