Why are there so many shallow lakes near the Yangtze and Han rivers in Hubei?

The prevalence of shallow lakes near the Yangtze and Han rivers in Hubei is primarily due to the region's unique geological history and ongoing landscape formation.

The area is situated on a vast alluvial plain that serves as the remnant of an old lake basin formed during the Pliocene Epoch, approximately 5.3 to 2.6 million years ago. Over time, this depression has been gradually filled with eroded red sandstone transported from Sichuan province.1

Because this filling-in process remains incomplete, the landscape is characterized by low-lying, flat, or gently undulating terrain—much of which sits less than 200 feet above sea level—that is dotted with innumerable shallow lakes. These lakes, along with various marshes and river channels, have historically functioned as a natural flood-regulation basin for the Yangtze and its tributaries, including the Han River, by absorbing excess water during periods of high flow.12