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New River (Mexico–United States)
The New River (Río Nuevo in Spanish) flows north from near Cerro Prieto, through the city of Mexicali, Baja California, Mexico, into the United States through the city of Calexico, California, towards the Salton Sea. The river channel has existed since pre-historic times; however, the river as known today was formed from a levee failure that resulted in massive flooding that re-created the Salton Sea. Today, the river flow is not natural, mostly consisting of agricultural runoff, municipal discharge and industrial dumping. The river has been referred to as the most severely polluted river of its size within the United States.〔 〕 Several projects have begun to reduce and mitigate the levels of pollution in the river, including upgrading sewage treatment infrastructure and enclosing the river channel.
==Flow==
The New River channel begins at a volcanic lake, near Cerro Prieto.〔 Today this lake feeds the Cerro Prieto Geothermal Power Station. The river flows north 15 miles (25 km) through Baja California and another 66 miles (100 km) through California into the Salton Sea, the largest lake in California. Flow at the border is approximately 200 ft³/s (6 m³/s), and about three times this flow at the Salton Sea because of collected agricultural discharges.
The New River’s flow is composed of waste from agricultural and chemical runoff from the farm industry irrigation in the U.S. (18.4%) and Mexico (51.2%), sewage from Mexicali (29%), and manufacturing plants operating in Mexico (1.4%). By the time the New River crosses the U.S./Mexico border near Calexico, California, the channel contains a stew of about 100 contaminants: volatile organic compounds, heavy metals (including selenium, uranium, arsenic and mercury), and pesticides (including DDT) and PCBs. The waterway also holds the pathogens that cause tuberculosis, encephalitis, polio, cholera, hepatitis and typhoid; levels for many of these contaminants are in violation of United States Environmental Protection Agency (EPA) and Cal/EPA standards by several hundredfold. Fecal coliform bacteria are at levels of 100,000 to 16 million colonies per milliliter at the border checkpoint (possibly more, as this is the measuring capacity threshold), far above the U.S.-Mexico treaty limit of 240 colonies.
The combined effects of increasing, highly polluted inflow from the New River and agricultural runoff have resulted in elevated bacterial levels and large algal blooms in the Salton Sea. With the lack of an outlet, salinity has increased by approximately 1% per year. Due to high selenium levels, the public was strictly advised to limit fish consumption from the Salton Sea in 1986, after which any amount was likely a health risk. Increasing water temperature, salinity and bacterial levels led to massive fish die-offs (1992, 1994, 1996, 1999, 2006, 2008), and created the ideal breeding grounds for avian botulism, cholera and Newcastle disease, which also led to massive avian epizootics from 1992–2008. Currently, the Salton Sea has a salinity of 4.4% (4.4 parts per 100), making it saltier than ocean water (3.5% for Pacific), and many species of fish are no longer able to reproduce or survive in the Salton Sea. It is now believed the tilapia may be the only fish species able to persist there for a limited time. Without restoration actions, the sea will likely increase in toxicity, and remain an ecological trap for avian species.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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