The Hardy River (Spanish: Río Hardy) is a 26-kilometer (16 mi)-long Mexican river formed by residual agricultural waters from the Mexicali Valley and running into the Colorado River. The river is believed to have been an ancient channel of the Colorado. In the 1800s, a sea captain (Captain Hardy) explored the Colorado River Delta, and noted that the main channel of the Colorado followed this course. Later in the 1880s, sea captains noted that the main channel of the Colorado had moved east, and this old channel became known as Hardy's Colorado.
In much earlier times, the Colorado River periodically flowed north into the Salton Sink, forming a large lake called Lake Cahuilla. Eventually, Lake Cahuilla would fill to about 30' above sea level, at which point the lake would overflow its banks near Cerro Prieto and flow south to the Sea of Cortez. During those times, the Rio Hardy would serve as the overflow channel for Lake Cahuilla.
The Rio Hardy is home to a variety of wildlife, including the mosquitofish and the sailfin molly.
The Hardy's wetlands are a nesting ground for the Snowy Egrets (Egretta thula). The wetlands and bird habitat are part of a protected Mexican Biosphere Reserve called the Reserva de la Biosfera del Alto Golfo de California y Delta del Rio Colorado, .
In recent years, the Hardy has become a drain for agricultural waters polluted with pesticides and fertilizers from the Mexicali Valley. The water quality in the Hardy is being monitored at Mexicali by the Centro de Investigacion en Alimentacion y Desarrollo A.C. to measure the effects of discharge from the Las Arenitas wastewater treatment plant.
- The State of Baja California: Hydrology
- Deciding About the Colorado River Delta, River Report, Water Education Foundation, Spring 1999, by S. Joshua Newcom
- E.P.A.: California-Baja California Regional Workgroup: California-Baja California Water
- A tribe without a river, by Celia Rosario Rivas and Luis Carlos Romero-Davis, Tucson Citizen, June 20, 2006
- Contaminants in Potential Prey of the Yuma Clapper Rail, U.S. Fish and Wildlife Service