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

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

, with its low

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

with respect to the

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

, 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 The Xi River (; ) or Si-Kiang is the western tributary of the Pearl River in southern China. It is formed by the confluence of the Gui and Xun Rivers in Wuzhou, Guangxi. It originates from the eastern foot of the Maxiong Mountain in Qujing C ...

(''West River'') in

Guangdong Guangdong (, ), alternatively romanized as Canton or Kwangtung, is a coastal province in South China on the north shore of the South China Sea. The capital of the province is Guangzhou. With a population of 126.01 million (as of 2020) ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

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 (PRD; ; pt, Delta do Rio das Pérolas (DRP)) 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-Mac ...

. The salinity level of

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

Zhuhai Zhuhai (, ; Yale: ''Jyūhói''), also known as Chuhai is a prefecture-level city located on the west bank of Pearl River estuary on the central coast of southern Guangdong province, People's Republic of China, on the southeastern edge of Pearl ...

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 specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...

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 {{Geology-stub