Shimsha is a river that flows in the state of Karnataka, India. It is one of the tributaries of the river Kaveri, which is one of the major rivers of South India. The river originates in the southern part of the Devarayanadurga hill in the Tumkur district of Karnataka and flows for about 221 km (137 mi). before joining the river Kaveri.
After originating in the Tumkur district, the river takes a southerly course and enters the Mandya district. In Mandya district, the river flows in a south-eastern direction and has a waterfall at Shimshapura in Malavalli Taluk. Just after Shimshapura it reaches the border of Chamarajanagar district where it joins the river Kaveri. The confluence of Shimsha and Kaveri is also near the Shivanasamudra falls. The total length of the river is 221 km (137 mi). and the river has a catchment area of 8469 km².
In its course the river is joined by other smaller rivers and streams such as Veeravaishnavi, Kanihalla, Chikkahole, Hebbahalla, Mullahalla and Kanva.
- Towns and cities
Maddur is a major town that lies on this river.
- Markonahalli Dam
Markonahalli Dam is a dam built across the river Shimsha in the Kunigal Taluk of Tumkur district. It was built by Krishnaraja Wodeyar IV, the king of Mysore under the guidance of his Diwan, Sir M Visweswaraiah. It was built to irrigate 6070 hectares of land and has a masonry structure of 139 m and a pair of earth dams extending to 1470 metres on either side. The reservoir has a catchment area of 4,103 km2 (1,584 sq mi) and can hold a volume of 68 million m³ of water at a full reservoir level of 731.57 m above the mean sea level. 27 species of fish, including 13 species of commercial fishes have been recorded in the reservoir with Puntius being the dominant species of fish found here. Cirrhinus reba and Labeo calbasu and other transplanted carps are also found here. However, the maintenance of the dam has been poor. In 2000, a part of the dam had to be demolished to prevent floods and save 25 villages. Water started overflowing the dam and only 1 crest gate could be opened. Nearly 150 feet of the dam was demolished to allow excess water to flow out.
Power generation 
Shimsha has a waterfall at Shimshapura in Malavalli Taluk. This is also the location of the Shimsha Hydro Electric Project which has an installed capacity of 17,200 kilowatts. It was the first ever hydro electric project in Asia. Kolar Gold Fields was supplied with the electricity generated in 1902. Three years later Bangalore was electrified. (Prajavani daily 16th Oct 08) The foundation stone for this project was laid by Krishnaraja Wodeyar IV, the king of Mysore in December 1937.
Sand mining 
The sand found on the river bed of the Shimsha river is mined and used for construction activities, sometimes illegally. Due to the environmental issues that can be caused by sand mining, this activity is currently banned.
Discharge of waste from towns and cities on the way are major contributors to pollution in the Shimsha. However, the Government is trying to clean up the river and has released funds for the same.
- "River systems of Karnataka". Online webpage of the Water Resources Department. Government of Karnataka. Retrieved 2007-08-26.
- "Mandya district". Online webpage of MapsofIndia.com. Retrieved 2007-08-26.
- "Incessant rain: Part of Markonahalli Dam broken open". Online Edition of The Hindu, dated 2000-10-11 (Chennai, India). 2000-10-11. Retrieved 2007-08-27.
- "Reservoir fisheries of India: Karnataka". Online webpage of FAO. Retrieved 2007-08-27.
- "100 years of hydel power in State". Online Edition of The Hindu, dated 2004-07-05 (Chennai, India). 2004-07-05. Retrieved 2007-08-26.
- "Stop sand mining at Shimsha river bed, HC tells K'taka Govt". Online webpage of OneIndia.in. Retrieved 2007-08-26.
- "Rs 2 cr to clean Shimsha". Online Edition of The Deccan Herald, dated 2005-06-07. Archived from the original on 2007-09-29. Retrieved 2007-08-26.