Salt tide is a phenomenon in which the lower course of a

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

, with its low

altitude Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum (geodesy), datum and a point or object. The exact definition and reference datum varies according to the context (e.g., aviation, geometr ...

with respect to the

sea level Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

, becomes salty when the discharge of the river is low during dry season, usually worsened by the result of astronomical high tide. The lower course Xijiang (''West River'') in

Guangdong ) means "wide" or "vast", and has been associated with the region since the creation of Guang Prefecture in AD 226. The name "''Guang''" ultimately came from Guangxin ( zh, labels=no, first=t, t= , s=广信), an outpost established in Han dynasty ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

was periodically affected and has been widely reported since 2004, for bringing shortage of fresh water supply to the western part of the

Pearl River Delta The Pearl River Delta Metropolitan Region is the low-lying area surrounding the Pearl River estuary, where the Pearl River flows into the South China Sea. Referred to as the Guangdong–Hong Kong–Macao Greater Bay Area in official documents, ...

. The salinity level of

tap water Tap water (also known as running water, piped water or municipal water) is water supplied through a Tap (valve), tap, a water dispenser valve. In many countries, tap water usually has the quality of drinking water. Tap water is commonly used f ...

Zhuhai Zhuhai; Yale romanization of Cantonese, Yale: ''Jyūhói''; Chinese postal romanization, also known as Chuhai is a prefecture-level city located on the west bank of the Pearl River (China), Pearl River estuary on the central coast of southern ...

was reported to be as high as 800 mg per litre in late February 2006, more than 3 times higher than the

World Health Organization The World Health Organization (WHO) is a list of specialized agencies of the United Nations, specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Gen ...

standard of 250 mg.

References

*"Fresh-water crisis looms for Macau - Salinity keeps rising despite assurances", ''South China Morning Post'', Page A7 Hong Kong & Delta, published Thursday, February 23, 2006. Hydrology Rivers Freshwater ecology {{hydrology-stub