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|Native name||Sungai Klang ( Malay)|
|Country||Selangor and Kuala Lumpur, Malaysia|
|• location||Kuala Seleh|
|• elevation||100 m (330 ft)|
|Strait of Malacca|
|Length||120 km (75 mi)|
|• average||50 m3/s (1,800 cu ft/s)|
|• left||Gombak River, Damansara River, Penchala River|
|• right||Kerayong River|
The Klang River ( Malay: Sungai Klang) is a river which flows through Kuala Lumpur and Selangor in Malaysia and eventually flows into the Straits of Malacca. It is approximately 120 km (75 mi) in length and drains a basin of about 1,288 km2 (497 sq mi). The Klang River has 11 major tributaries.
Because the river flows through Klang Valley, which is a heavily populated area of more than four million people, it is considerably polluted, because of deep siltation caused by human waste from informal settlers of the riverbank and even from some business establishments without septic tanks or sewage treatment plants and by soil carried by mudflows from mountains. Heavy development has narrowed certain stretches of the river to the point that it resembles a large storm drain in some places. This contributes to flash floods in Kuala Lumpur, especially after heavy rain.
The Klang River originates from the Klang Gates Quartz Ridge in Gombak, near the border with Pahang, 25 kilometres (16 mi) northeast of Kuala Lumpur. It is joined by 11 major tributaries. These include the Gombak River, Batu River, Kerayong River, Damansara River, Keruh River, Kuyoh River, Penchala River and Ampang River. It flows into the Straits of Malacca to the west.
The river's confluence with the Gombak River gave rise to the name of Kuala Lumpur, Malaysia's capital city. Kuala Lumpur means "muddy estuary", and this definition almost applies to the modern time because of siltation mentioned above. It is also thought that Klang town is named after the river.
Kuala Lumpur is situated at the point where the Gombak River flows into the Klang River. The confluence is located behind Masjid Jamek. It then flows south-west through Brickfields, Bangsar, Lembah Pantai, Old Klang Road and Jalan Puchong, then become the border of Petaling Jaya and Subang Jaya until PJS7, later passing UEP Subang Jaya, before making a U-turn in Puchong and Putra Heights.
Malaysia's biggest sea port, Port Klang, is also situated at the estuary of the Klang River.
Historically, Kuala Lumpur has often suffered from severe flooding from the river water overflowing the banks. In 1926, a particularly severe flood hit Kuala Lumpur, and work on the river then began in an attempt to reduce the risk of flooding. Part of the Klang River below the Gombak-Klang confluence was straightened, a channel (part of which runs beside the present Jalan Syed Putra) with flood retention banks was dug to divert the river. This project was completed in 1932. 
Efforts in controlling flood water is continuing process. Kuala Lumpur Flood Mitigation is a project to mitigate flash floods affecting Kuala Lumpur. In include diverting flood water from the Gombak River into a few stormwater ponds located in Batu, Jinjang and Kepong. 
The SMART Tunnel (Stormwater Management and Road Tunnel) is part of Kuala Lumpur Flood Mitigation Project and functions to reduce both traffic congestion and flooding. It is a submerged tunnel which can carry both vehicular traffic as well as storm runoff on a lower level. When regular drainage infrastructure is overwhelmed, vehicles are evacuated from the tunnel and the entire tube is used as a gigantic storm drain to prevent Kuala Lumpur from flooding. It diverts water flow from the Kampung Berembang Lake, near the Klang River, to Taman Desa Lake, which is near the Kerayong River (one of the Klang River's tributaries). Water flow can also go the opposite direction, from the Kerayong River to the Klang River. SMART opened in May 2007.
In 2010 Selangor has a stimulus bill that included money to help rehabilitate it. The river's condition has been described as "between critical and bad" by Gareth Jones of Wessex Water, a UK-based company that is participating in the project. Kamal Zaharin, the project mastermind, states that the plans include river cleaning, new source of drinking water, environmental protection, flood mitigation, commercial, tourism and land development activities. Gareth Jones also stated that they plan on tapping groundwater in order to have a source of water that is not the sea. 
The project has been estimated to require 15 years and attract 15 billion dollars of investment. 
- Sharifah Munirah Alatas (2011). "Governance and Freshwater in the Greater Kuala Lumpur Area/Klang Valley: Success or Failure?" (PDF). Akademika. 81 (3): 95–102. Archived from the original (PDF) on 4 March 2016.
- Anil Netto (24 February 2006). "Malaysia: Fighting the Flow of River Privatisation". Inter Press Service. Retrieved 28 June 2022.
- Wani Muthiah (2 July 2006). "Three Rivers in Selangor to Go Private Soon". The Star. p. 3.
- Gullick, J. M. (1983). The Story of Kuala Lumpur, 1857–1939. Eastern Universities Press (M). pp. 252–253. ISBN 978-967-908-028-5.
- "Flood Mitigation Program". Ministry of Natural Resources and Environment. Archived from the original on 22 December 2007. Retrieved 11 December 2007.
- Ng, Angie (20 March 2010). "Selangor to Clean up Klang River". The Star Online. Archived from the original on 17 December 2011. Retrieved 25 March 2011.