Bass Lake, formerly known as Crane Valley Reservoir, is a man-made lake located in Madera County, California, within the Sierra National Forest, approximately 14 miles (23 km) south of Yosemite National Park.[3] The lake was formed by the construction of Crane Valley Dam on Willow Creek, a tributary of the San Joaquin River. Completed in 1910, the 145-foot (44 m) concrete gravity dam was built to generate hydroelectric power. Today, Bass Lake supports energy production, recreation, and diverse ecological habitats.
The name "Crane Valley" dates back to 1851, when early explorers misidentified great blue herons as cranes in the region’s wetlands.[4] Hydroelectric development began in 1895 under the San Joaquin Electric Company, which constructed an earthen dam in 1901. The project was later expanded by San Joaquin Light & Power, culminating in the completion of the present-day concrete dam in 1910.[5] The name "Bass Lake" became common after bass were introduced to the reservoir following pollution from upstream logging operations.
Dam and Infrastructure
Construction and Expansion
The dam has been modified multiple times. Enlargements occurred in 1905 and again in 1910, bringing the structure to its current height of 145 feet (44m).
Seismic Retrofit
Between 2009 and 2012, PG&E undertook a $63 million seismic retrofit to improve structural safety.[6] The project included placement of 300,000 cubic yards (230,000m3) of rock and raised the dam crest by 8 feet (2.4m).[7]
Hydroelectric Operations
Crane Valley Dam is the upper reservoir of the Crane Valley Hydroelectric Project, which includes five powerhouses: Crane Valley, San Joaquin No. 3, No. 2, No. 1A, and A.G. Wishon.[8] The system generates a combined 28.7 megawatts, supplying electricity to approximately 22,000 homes.[9] Since 1978, regulated releases have supported summer recreation and fall irrigation via the Madera Irrigation District.[10] The Federal Energy Regulatory Commission (FERC) licensed the project in 2003, mandating minimum flow requirements, habitat protections, and public access.[11] In 2020, PG&E announced plans to sell the project under its existing license and obligations.
Environmental and Ecological Impact
Ecological Changes
The reservoir inundated a portion of Willow Creek, converting meadow and stream ecosystems into lake habitat. Warmwater species such as bass, sunfish, and trout were introduced. Agencies expressed concern about downstream impacts on native fish like hardhead and Sacramento sucker. The presence of bald eagles, black bears, deer, and waterfowl has also been documented. Threatened species identified during relicensing prompted specific habitat protections.[12]
Streamflow Management
Crane Valley Dam regulates all flow in North Fork Willow Creek. Historically seasonal, the creek was often dry downstream. PG&E is now required to release a continuous minimum flow of 2 cubic feet per second (cfs), with additional seasonal “flushing flows” to support riparian ecosystems and trout populations.[12] These measures have helped offset some of the reservoir’s ecological impacts.[12]
Water Quality
Bass Lake maintains generally good water quality and is not listed as impaired under the Clean Water Act 303(d) program.[13] Mercury levels in water and fish tissue remain below thresholds for concern.[14] While flagged for further review in 2016, the lake was not designated as impaired due to insufficient data.[13] Other indicators, including nutrient levels and dissolved oxygen, suggest a mesotrophic condition. Summer stratification occurs, but bottom oxygen levels are maintained by outlet circulation. The lake meets drinking water standards and has not experienced harmful algal blooms as of 2025.[14]
Climate, Drought, and Fire Impacts
During the 2012–2016 drought, water levels dropped to 45–50% of capacity, stressing aquatic habitats and reducing recreational access. Shallow zones warmed significantly, affecting cold-water fish and wetland seeps. Managers extended boat ramps and posted hazard warnings.[15]
In contrast, wet winters like 2016–2017 brought rapid inflows, prompting increased outflows to prevent flooding. Climate change is expected to increase variability through reduced snowpack and more frequent rain-on-snow events.
Ongoing Management
Bass Lake remains a multi-use resource with collaborative oversight. The U.S. Forest Service manages public access and recreation, while PG&E maintains dam operations. Ongoing efforts include sediment monitoring, invasive species prevention, and wildlife surveys. The Bass Lake Task Force coordinates interagency efforts to promote long-term ecological and recreational sustainability.
↑ U.S. Geological Survey (2009). "Feature Detail Report: Bass Lake". Geographic Names Information System (GNIS). U.S. Department of the Interior. Retrieved 2009-03-13.
↑ Ritzman, David; Makdisi, Faiz; de Larios, Joseph; Sun, Joseph; Ahlgren, Charles (May 2, 2013). "Seismic Retrofit of Crane Valley Dam". Missouri University of Science and Technology. Retrieved November 22, 2021.
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