Marble Rock Milldam Reservoir Report

Last Updated: December 12, 2025

Marble Rock Milldam, located in Floyd County, Iowa, along the Shell Rock River, was completed in 1913 for the primary purpose of recreation.


°F

°F

mph

Wind

%

Humidity

Summary

This gravity dam stands at a height of 15 feet with a length of 187 feet, creating a reservoir with a storage capacity of 836 acre-feet. The dam is state-regulated by the Iowa Department of Natural Resources, ensuring that it meets safety and environmental standards.

Despite being classified as having a low hazard potential, Marble Rock Milldam has a moderate risk assessment rating. While the dam has not been inspected since 1989 and is currently not rated in terms of its condition assessment, it remains a popular spot for recreational activities such as fishing, boating, and picnicking. The dam also serves as a reminder of the region's history and the importance of managing water resources in a sustainable way.

As an important landmark in the area, Marble Rock Milldam continues to attract visitors and water resource enthusiasts who appreciate its historical significance and its role in providing recreational opportunities. With its picturesque location and serene surroundings, the dam serves as a reminder of the intersection between human development and environmental stewardship, prompting discussions about the importance of maintaining and monitoring water infrastructure for future generations to enjoy.

Year Completed

1913

Dam Length

187

Dam Height

15

River Or Stream

SHELL ROCK RIVER

Primary Dam Type

Gravity

Surface Area

110

Drainage Area

1318

Nid Storage

836

Hazard Potential

Low

Foundations

Rock, Soil

Nid Height

15
       
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.