<P> The original version of the plan proposed to divert water from the Trinity River in northern California to reduce Southern California's dependence on the Colorado, allowing more water to be pumped, by exchange, to central Arizona . Because of the large amount of power that would be required to pump Colorado River water to Arizona, the CAP originally included provisions for hydroelectric dams at Bridge Canyon and Marble Canyon, which would have flooded large portions of the Colorado within the Grand Canyon and dewatered much of the remainder . When these plans were publicized, the environmental movement--still reeling from the Glen Canyon controversy--successfully lobbied against the project . As a result, the Grand Canyon dams were removed from the CAP agenda, the boundaries of Grand Canyon National Park were extended to preclude any further development in the area, and the pumping power was replaced by the building of the coal - fired Navajo Generating Station near Page, Arizona, in 1976 . The resulting Central Arizona Project (CAP) irrigates more than 830,000 acres (3,400 km) and provides municipal supplies to over 5 million people from Phoenix to Tucson using water from the Colorado River . </P> <P> Historically, the Colorado transported from 85 to 100 million short tons (77,000,000 to 91,000,000 t) of sediment or silt to the Gulf of California each year--second only to the Mississippi among North American rivers . This sediment nourished wetlands and riparian areas along the river's lower course, particularly in its 3,000 - square - mile (7,800 km) delta, once the largest desert estuary on the continent . Currently, the majority of sediments carried by the Colorado River are deposited at the upper end of Lake Powell, and most of the remainder ends up in Lake Mead . Various estimates place the time it would take for Powell to completely fill with silt at 300 to 700 years . Dams trapping sediment not only pose damage to river habitat but also threaten future operations of the Colorado River reservoir system . </P> <P> Reduction in flow caused by dams, diversions, water for thermoelectric power stations, and evaporation losses from reservoirs--the latter of which consumes more than 15 percent of the river's natural runoff--has had severe ecological consequences in the Colorado River Delta and the Gulf of California . Historically, the delta with its large freshwater outflow and extensive salt marshes provided an important breeding ground for aquatic species in the Gulf . Today's desiccated delta, at only a fraction of its former size, no longer provides suitable habitat, and populations of fish, shrimp and sea mammals in the gulf have seen a dramatic decline . Since 1963, the only times when the Colorado River has reached the ocean have been during El Niño events in the 1980s and 1990s . </P> <P> Reduced flows have led to increases in the concentration of certain substances in the lower river that have impacted water quality . Salinity is one of the major issues and also leads to the corrosion of pipelines in agricultural and urban areas . The lower Colorado's salt content was about 50 parts per million (ppm) in its natural state, but by the 1960s, it had increased to well over 2000 ppm . By the early 1970s, there was also serious concern about salinity caused by salts leached from local soils by irrigation drainage water, which were estimated to add 10 million short tons (9,100,000 t) of excess salt to the river per year . The Colorado River Basin Salinity Control Act was passed in 1974, mandating conservation practices including the reduction of saline drainage . The program reduced the annual load by about 1.2 million short tons (1,100,000 t), but salinity remains an ongoing issue . In 1997, the USBR estimated that saline irrigation water caused crop damages exceeding $500 million in the U.S. and $100 million in Mexico . Further efforts have been made to combat the salt issue in the lower Colorado, including the construction of a desalination plant at Yuma . In 2011, the seven U.S. states agreed upon a "Plan of Implementation", which aims to reduce salinity by 644,000 short tons (584,000 t) per year by 2030 . In 2013, the Bureau of Reclamation estimated that around $32 million was spent each year to prevent around 1.2 million tons of salt from entering and damaging the Colorado River . </P>

Does the colorado river still reach the ocean