section_path: Hydrology/Degradation of the river
section_name: Degradation of the river
paragraph_text: Degradation of the river
  
  Beginning in the 1950s, dams and dikes were built for flood control, land reclamation, irrigation, and control of diseases vectors such as blood flukes that caused Schistosomiasis. More than a hundred lakes were thusly cut off from the main river. There were gates between the lakes that could be opened during floods. However, farmers and settlements encroached on the land next to the lakes although it was forbidden to settle there. When floods came, it proved impossible to open the gates since it would have caused substantial destruction. Thus the lakes partially or completely dried up. For example, Baidang Lake shrunk from 100 square kilometers (39 sq mi) in the 1950s to 40 square kilometers (15 sq mi) in 2005. Zhangdu Lake dwindled to one quarter of its original size. Natural fisheries output in the two lakes declined sharply. Only a few large lakes, such as Poyang Lake and Dongting Lake, remained connected to the Yangtze. Cutting off the other lakes that had served as natural buffers for floods increased the damage done by floods further downstream. Furthermore, the natural flow of migratory fish was obstructed and biodiversity across the whole basin decreased dramatically. Intensive farming of fish in ponds spread using one type of carp who thrived in eutrophic water conditions and who feeds on algae, causing widespread pollution. The pollution was exacerbated by the discharge of waste from pig farms as well as of untreated industrial and municipal sewage. In September 2012, the Yangtze river near Chongqing turned red from pollution. The erection of the Three Gorges Dam has created an impassable "iron barrier" that has led to a great reduction in the biodiversity of the river. Yangtze sturgeon use seasonal changes in the flow of the river to signal when is it time to migrate. However, these seasonal changes will be greatly reduced by dams and diversions. Other animals facing immediate threat of extinction are the baiji dolphin, narrow-ridged finless porpoise and the Yangtze alligator. These animals numbers went into freefall from the combined effects of accidental catches during fishing, river traffic, habitat loss and pollution. In 2006 the baiji dolphin became extinct; the world lost an entire genus.
  
  In 2020, a sweeping law was passed by the Chinese government to protect the ecology of the river. The new laws include strengthening ecological protection rules for hydropower projects along the river, banning chemical plants within 1 kilometer of the river, relocating polluting industries, severely restricting sand mining as well as a complete fishing ban on all the natural waterways of the river, including all its major tributaries and lakes.