Big Bear Lake is a popular destination in the San Bernardino Mountains, known for its scenic beauty, year-round recreation, and clear alpine waters. This large body of water, central to the mountain community, appears to be a natural feature of the high-altitude landscape. However, the lake’s origins are deeply tied to human engineering and the agricultural needs of Southern California. The question of whether Big Bear Lake is a product of nature or human intervention is answered by looking closely at its history.
The Origin of Big Bear Lake
Big Bear Lake is not a natural lake; it is a man-made reservoir created by damming the western outlet of the mountain valley. A reservoir is an artificial lake, created to store water for various uses, and Big Bear Lake serves this exact function. It is classified as a reservoir because its basin was artificially deepened and its water level is maintained by a large, constructed dam structure.
The water filling the reservoir is entirely natural, primarily sourced from snowmelt and direct precipitation within the surrounding watershed. While the water is natural, the permanent, deep body of water itself is the result of engineering, not geology. The dam transformed a seasonally wet, marshy area into a large, stable lake.
The Historical Purpose and Construction
The creation of Big Bear Lake was driven by the need for reliable water in the agricultural areas far below the mountains. The primary purpose was supplying water for irrigation, specifically for the citrus groves in the Redlands area of the lower valleys. A Redlands farmer named Frank E. Brown spearheaded the project, recognizing the potential of the high-altitude valley to capture and store mountain runoff.
Construction of the first dam, known as the “Old Bear Valley Dam,” began in 1883 and was completed in 1884. This single-arch granite dam was a remarkable engineering feat for its time, and upon its completion, it created what was then considered the world’s largest man-made lake. Engineers were initially skeptical that the thin structure would hold the pressure of the stored water.
Despite its success, the original dam proved inadequate for the growing demand, holding only about 25,000 acre-feet of water. This led to the lake occasionally drying up completely during summer months around the turn of the century. A higher dam was necessary to ensure a consistent water supply, leading to the construction of a new, multiple-arch concrete dam approximately 300 feet downstream from the original.
This replacement dam, designed by engineer John S. Eastwood, was completed in 1912 and stood 20 feet higher than the first structure. The new dam nearly tripled the lake’s capacity, increasing its storage to around 73,000 acre-feet and securing the water supply for the valley’s development and downstream agriculture.
The Natural Geography Before the Dam
The landscape that existed before the construction of the 1884 dam was vastly different from the lake seen today. The area was originally known as Bear Valley, a high-elevation alpine valley situated at about 6,750 feet. This valley was not a deep, permanent lake, but rather a large, marshy meadow fed by seasonal creeks and snowmelt.
The valley floor was nearly flat and functioned as a vast, natural catchment basin that would become saturated and marshy during the wet season. Water would collect temporarily, but there was no significant natural barrier to create a deep, year-round body of water.
The dam dramatically transformed this ecosystem, converting the seasonal valley floor and forested areas into a permanent, deep lake with a maximum depth of 72 feet. The construction flooded over 9,000 trees and changed the fundamental geography from a marshy valley into the large, seven-mile-long reservoir we recognize today.