The river was originally alluvial, meaning its banks and bed were formed from loose sediments and rock that allowed it to change its path depending on water flow and season. Up until the early 1800's, the river actually flowed into the Pacific near Marina Del Ray, but a particularly severe flash flood in 1825 diverted the river all the way to Long Beach, where it has remained since.
The Los Angeles River was the LA Basin's main source of drinking water until the Los Angeles Aqueduct opened in 1913, water from the Owens River being pumped over the Sierra Nevada mountain range and into the city. Although the river was fairly dry for most of the year, winter rains often brought with them dramatic and unpredictable flash floods well into the 1930s. After a devastating flood in 1938, Angelenos began to demand flood control measures, leading to the creation of an ambitious project to both encase the riverbed in concrete to prevent it from changing course, and to regulate flow by building the Sepulveda Dam. The Army Corps of Engineers would spend the next 30 years essentially turning the river into a man-made storm drain.
Now, work on the Los Angeles River has moved from flood control to conservation, as advocacy groups and individuals take on the task of preserving and restoring the river and its wildlife. The Sepulveda Basin has become known not just for its dam, but for its recreational space and ecological diversity. The Los Angeles River itself is increasingly the site of artistic, social, and educational activity, once becoming a lifeline linking a growing and diverse population.