Whale Rock Reservoir Report

Last Updated: December 5, 2025

Whale Rock is a natural landmark located in San Luis Obispo County, California.


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Summary

The rock is a volcanic plug that rose from the ocean floor over 25 million years ago. It is approximately 361 feet tall and dominates the landscape of the nearby town of Cayucos. The hydrology of the area is determined by the Whale Rock Reservoir, which is located just west of the rock. The reservoir provides surface water flow to the area through the Los Osos Creek watershed. The water in the reservoir comes from a combination of surface flow and snowpack melt from the surrounding mountains. The water from the reservoir is used for agricultural purposes in the surrounding area. Recreational activities, such as hiking and fishing, are also popular in the area.

Reservoir Details

24hr Change None%
Percent of Normal None%
Minimum
Maximum
Average
Dam_Height 193
Hydraulic_Height 176
Drainage_Area 20.8
Year_Completed 1960
Nid_Storage 40662
Hazard_Potential High
Primary_Dam_Type Earth
River_Or_Stream Old Creek
Surface_Area 594
Dam_Length 850
Nid_Height 193
       
Seasonal Comparison
Storage Levels
Pool Elevation Levels
Top Conserv Storage Levels
Inflow Levels

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.