River delta slope offshore, waves will make river deltas smoother. Waves can also be responsible for carrying sediments away from the river delta, causing the delta to retreat. For deltas that form further upriver in an estuary, there are complex yet quantifiable linkages between winds, tides, river discharge, and delta water levels. Erosion is also an important control in tide-dominated deltas, such as the Ganges Delta, which may be mainly submarine, with prominent sandbars and ridges. This tends to produce a "dendritic" structure. Tidal deltas behave differently from a river- and wave-dominated deltas, which tend to have a few main distributaries. Once
Pearl River Delta brown smog. This has a strong effect on the pollution levels in the delta. Pollution is a great risk to the Chinese white dolphins that inhabit the area. On March 22, 2007 the World Bank approved a $96 million loan to the PRC government to reduce water pollution in the Pearl River Delta. On December 23, 2008 it was announced that ¥48.6 billion (about $7.1 billion) will be spent on the river by mid-2010 to clean up the river's sewage problems quoted by Zhang Hu, the director of Guangzhou municipal bureau of water affairs. The city will build about 30