Olson Reservoir (Mark) Reservoir Report

Last Updated: December 13, 2025

Olson Reservoir (Mark), also known as Mark Olson Dam, is a private water resource located in Polk County, Oregon.


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Summary

Completed in 1988, this earth dam serves primarily for irrigation purposes, with a storage capacity of 46 acre-feet and a normal storage level of 45.5 acre-feet. The reservoir covers a surface area of 4.2 acres and is fed by the Ash Swale tributary.

With a significant hazard potential, Olson Reservoir (Mark) stands at 25 feet in height and has a maximum discharge of 50.4 cubic feet per second. The dam features a slide (sluice gate) outlet gate for water release. Regular inspections are carried out, with the last one conducted in April 2019, and the reservoir meets state regulations for permitting, inspection, and enforcement. The location of this reservoir, near the city of McCoy, offers a serene setting for water resource and climate enthusiasts to explore and appreciate the vital role it plays in supporting local irrigation needs.

Year Completed

1988

Dam Length

360

Dam Height

25

River Or Stream

ASH SWALE, TRIB TO

Primary Dam Type

Earth

Surface Area

4.2

Hydraulic Height

22

Drainage Area

0.18

Nid Storage

46

Structural Height

25

Outlet Gates

Slide (sluice gate)

Hazard Potential

Significant

Nid Height

25
       
Seasonal Comparison

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.