The dam was built as part of the San Juan-Chama Project, which transfers water from the San Juan River basin through the Azotea Tunnel under the Continental Divide into Willow Creek, where it is stored in Heron Reservoir as part of the Colorado River Storage Project. The dam is located on Willow Creek near the creek's confluence with the Rio Chama. Construction was completed in 1971. The outlet works at El Vado Dam, just downstream from Heron Dam, were enlarged as part of the San Juan-Chama Project so releases from Heron Reservoir could pass unimpeded through the dam. The capacity of the El Vado outlet works was increased to pass per second.
Structure
The reservoir lies at an elevation of above sea level. The earthfill dam is long and high. Heron Dike, one mile northwest of the dam, helps contain the reservoir. It has a concrete crest spillway with an open chute with a discharge capacity of per second. The dam's outlet works include an intake structure, diameter concrete-lined upstream tunnel, gate chamber, modified horseshoe concrete-lined downstream tunnel, and a stilling basin. The discharge capacity is per second at a reservoir elevation of. When filled, the reservoir covers. The maximum safe storage capacity is. Downstream channel capacity is about per second.
Operations
The dam was built strictly for storage and delivery of San Juan-Chama Project water for municipal, domestic, industrial, recreation, irrigation, and fish and wildlife purposes. The water is diverted to New Mexico as agreed under the Colorado River and Upper Colorado River Compacts. The amount of water diverted each year, and the way in which it is used, are subject to well-defined agreements. Flows of "native" or "natural" water from Willow Creek and from the Rio Chama upstream of the dam are measured and bypassed through the reservoir. The dam provides up to of San Juan-Chama water annually to maintain the recreation pool at Cochiti Reservoir. The dam can supply about of San Juan-Chama water annually to users with reasonable certainty. There is no carry-over provision: contractors must take delivery of their water by December 31. This means that contractors such as the City of Albuquerque or the Middle Rio Grande Conservancy District often withdraw their water and arrange to store it in downstream reservoirs such as El Vado, Abiquiu, Jemez Canyon, and Elephant Butte.
