WWF released the World’s Top 10 Rivers at Risk report right before World Water Day 2007 in March but it’s worth the second mention on Earth Day.

Note: All the river diagrams shown below come from the WWF report. Click on the photographs to go see larger versions on flickr.

1. Salween (Asia, length: 2,800 Km).

The Salween is one of the few long rivers in the world that runs freely from source to sea. According to the WWF, dam construction is the single greatest threat to the river. China is planning up to 13 large hydropower projects in a cascade, that would truncate the river into a series of channels and reservoirs. Myanmar’s government also has several medium to large dam projects in the works. The biggest and most advanced project is the 228m high Tasang Dam, slated to be the tallest dam in Southeast Asia.

Photo by Natalie Behring from Flickr

2. Danube (Europe, length: 2,780 Km).

The Danube’s river basin is about twice the size of California and covers part or all of these 19 countries: Albania, Austria, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Germany, Hungary, Italy, Macedonia, Moldova, Poland, Romania, Serbia, Montenegro, Slovakia, Slovenia, Switzerland and Ukraine. Navigation and associated infrastructure projects are some of the primary causes of environmental degradation along the Danube. A significant cause for concern is the EU’s plan to develop the Trans-European Networks for Transport (TEN-T) “Corridor VII” along the river. The program’s aim is to cut out navigation ‘bottlenecks’ as well as improve inland navigation between Eastern and Western Europe. This means straightening, deepening, dredging, construction of hydraulic modifications, new canals, and other genuine badness for the riverine ecosystem.

Photo by CruisAir from Flickr

3. La Plata (South America: 3,740 Km from the longest tributary of the Paraná)

The La Plata basin is the second largest river basin in South America, spanning five countries: Argentina, Bolivia, Brazil, Paraguay, and Uruguay.

The threats from dams and navigation on the La Plata are intense. For example, on the Paraná River, the Itaipu Dam, the largest in the world,28 flooded approximately 100,000 ha of land, and destroyed significant aquatic habitat including the Guaíra Falls (WWF 2005d). The basin faces the second greatest number of planned dams in the world: 27 large dams29, of which six are under construction.

Photo by togno2006 from Flickr

4. Rio Grande - Rio Bravo (US/Mexico, Length: 3,033 Km)

The major threat to the Rio Grande/Rio Bravo is over-extraction. It is being sucked dry for irrigation. “Between February and June 2001, the river failed to reach the Gulf of Mexico”.

Historically, flows passing through Big Bend have varied considerably (NPS 2006), but by the time the Rio Grande leaves El Paso, a city less than one third the length of the river at this confluence of the Rio Conchos, so much water has been diverted that the riverbed between El Paso and Presidio/Ojinaga often lies dry (NPS 2006).

Photo by Cirem from Flickr

5. Ganges (Asia, Length: 2,507 Km)

The Ganges river basin flows from the central Himalayas to the Bay of Bengal, covering sections of Nepal, India, China and Bangladesh. The basin covers a whopping 30% of India’s land area. Threats to the Ganges include water extraction and dams.

In India, barrages control all of the tributaries to the Ganges and divert roughly 60% of river flow to large scale irrigation (Adel 2001). India controls the flow of the Ganges into Bangladesh with over 30 upstream water diversions. The largest, the Farraka Barrage, 18 Km from the border of Bangladesh, reduced the average monthly discharge of the Ganges from 2,213 m3/s to a low of 316m3/s [14%] (Goree 2004; FAO 1999).

Photo by dwrawlinson from Flickr

6. Indus (Asia, Length: 2,900 Km)

The Indus river basin covers parts of Afghanistan, Pakistan, India and China. It is a critical water source for Pakistan, as it irrigates 80% of its 21.5 million ha of agricultural land. An estimated 70-80% of the river’s water is derived from Himalayan glaciers.

The Indus basin is already suffering from severe water scarcity due to overextraction for agriculture, causing salt water intrusion in the delta (WRI 2003). In 1995, the Indus River already supplied much less water per person than the minimum recommended by the United Nations (UN)49 and by 2025 is predicted to suffer even more severe water scarcity50 (Revenga et al. 2000).

Photo by Michael Foley from Flickr

7. Nile (East Africa, Length: 6,695 Km; World’s longest river)

The Nile River Basin is about the size of India and spans 10 African countries: Sudan, Ethiopia, Egypt, Uganda, Tanzania, Kenya, Rwanda, Burundi, Democratic Republic of Congo, Eritrea.

Due to heavy human extraction and high evaporation, the Nile river basin and its inhabitants are especially sensitive to climate change. Current water withdrawal for irrigation is so high, that despite its size, in dry periods, the river does not reach the sea (WWF 2004c). In addition, along its 3,000 km course through arid northern Sudan and southern Egypt, the Nile loses a huge amount of water to evaporation (United Nations Environment Programme (UNEP) 1993). This makes water supply extremely sensitive to temperature and precipitation changes. Climate warming models provide diverging pictures of future river flows in the Nile from a 30% increase to a 78% decrease (IPCC 1997; IPCC 2001; Olago 2004). In addition, saltwater intrusion into coastal freshwater resources (including aquifers) is likely to increase as a result of sea-level rise due to climate warming (IPCC 2001; Miller no date) and would further reduce the availability of freshwater in the delta region.

Photo by DIDS from Flickr

8. Murray-Darling (Australia, Length: 3,370 Km)

The Murray-Darling River Basin feeds parts of 4 Australian states (Queensland, New South Wales, South Australia and Victoria).

In the past century, native fish species in the Murray-Darling basin have undergone a serious decline in distribution and abundance, while that of invasive species has significantly increased (MDBC 2005). In fact, native fish populations are roughly 10% of their pre-European settlement levels (Murray Darling Basin Ministerial Council 2003; Philips 2003 in Barrrett 2004). Nine of the 35 native fish species are nationally ‘threatened’, two are critically endangered, and 16 are threatened under state jurisdictions

Photo by jayjuice from Flickr

9. Mekong (Asia, Length: roughly 4,600 Km)

The Mekong River rises in the mountains of China’s Qinghai province, flowing south to form the border between Laos and Myanmar and most of the Thai Lao border. It moves through Cambodia and southern Vietnam into a rich delta, which empties to the South China Sea.

Unlike many major rivers in Asia, this river and its flood regime are relatively intact (Revenga et al. 2000). As a result, the lower Mekong basin is the most productive river fishery in the world (MRC 2004 in WWF 2004). Freshwater fisheries here have a commercial value exceeding US$1.7 billion and provide 80% of the animal protein consumed by 55 million inhabitants (Van Zalinge et al.2003).

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Despite the productivity of the Mekong, the threat of over-fishing is high because of the huge scale of subsistence fishing, the majority of which goes unrecorded,as well as poor fishing practices.

Photo by Farl from Flickr

10. Yangtze (China, Length: 6,300 Km)

The Yangtze River Basin covers 20% of China’s land mass. It accounts for 40% of China’s freshwater resources, over 70% of the country’s rice production, 50% of its grain, over 70% of fishery production, and 40% of the nation’s GDP.

Rivaling the impact of the Three Gorges Dam, this basin faces unprecedented pollution as a result of rapid, large-scale industrial and domestic development, and agricultural runoff.

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Over the last 50 years, there has been a 73% increase in pollution levels from hundreds of cities, in the main stem of the Yangtze River (WWF 2005h).
The annual discharge of sewage and industrial waste in the river has reached about 25 billion tons, which is 42% of the country’s total sewage discharge, and 45% of its total industrial discharge (WWF 2005h; Fang and Zhou 1999 in Pu 2003).

Photo by TimS from Flickr

Bonus Photo since I picked a not so pretty one of the Yangtze. The Li River

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