A basin for a giant
Dongting Lake is China's second-largest freshwater lake, but this ranking is part of its story. Its area and volume are in constant flux, governed by a dramatic seasonal flood pulse. In the dry season, from October to April, the lake's surface area is typically around 2,820 square kilometers. During the summer monsoon season, between June and October, the lake swells to absorb floodwaters from the Yangtze River, expanding its surface area to as much as 20,000 square kilometers. This eightfold increase in size is a result of its unique relationship with the Yangtze, for which it is a retention basin.
four major rivers: the Xiang, Zi, Yuan, and Li—flow into Dongting from the south and west, but its primary water exchange is with the Yangtze. During the summer floods, up to two-fifths of the Yangtze's water can pour into the lake, raising its level by as much as 15 meters. This inflow carries enormous quantities of nutrient-rich sediment, which historically made the surrounding lands exceptionally fertile. This process of expansion and contraction drives the entire ecosystem, dictating the life cycles of the flora and fauna that depend on it. Historically, the lake was much larger, known as the "Eight-hundred-li-Dongting," but centuries of sedimentation and land reclamation for agriculture have reduced its permanent size.