The Truckee-Carson Irrigation District (TCID) is a political subdivision of the State of Nevada, which operates dams at Lake Tahoe, on the Truckee River and Lake Lahontan as well as 380 miles (610 km) of canals and 340 miles (550 km) of drains in support of agriculture in Lyon County and Churchill County.
Diversion of water by the TCID from the Truckee River has caused a reduction in the level of Pyramid Lake, and endangered the endemic species of fish that live in it. In the mid 1980s the United States Environmental Protection Agency initiated development of the DSSAM Model to analyze effects of variable Truckee River flow rates and water quality upon these endangered fish species.