Even before construction began on the 3 Gorges Dam the Yangtze River was already suffering from extreme pollution but the addition of the dam has increased pollution levels. One reason is the use of commercial fertilizers, another is sewage from passenger boats that tour the river and reservoir (Yangtze Pollution Irreversible) and finally and possibly most serious is the increased greenhouse gas emissions from decaying vegetation.
Farming has long been a fruitful endeavor along the Yangtze River due to its frequent flooding. The flooding deposits nutrient rich silt from the river onto farmland. Since the reservoir is intended to limit flooding, the farmland that is still available will have to utilize commercial fertilizers for their crops. These fertilizers often contain cancer-causing nitrates that will runoff into surface water and will also be absorbed into ground water (Min). Another cause of pollution comes from the passenger boats touring the area. Tourism was a promoted benefit of the dam but it comes at a price since the tour boats release sewage into the water (Min) and that is a primary pollutant of the reservoir. Fertilizers and sewage are common pollutants but the third pollutant comes as a surprise since most people believe hydroelectricity to be clean energy and that is certainly not the case. A major problem with hydroelectric dams in general is that they are not the clean energy that everyone believes them to be. They produce significant amounts of greenhouse gas emissions. The pollution