Margeson Lake Reservoir Report

Last Updated: December 5, 2025

Margeson Lake, also known as Johnsen Lake, is a private water resource located in Forsyth, Georgia, specifically in the Cumming Community.


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Summary

The dam, completed in 1960, stands at a height of 25 feet and has a storage capacity of 73 acre-feet, with a primary purpose of recreation. The lake covers an approximate surface area of 6 acres and is fed by the Sawmill Branch river or stream.

Despite being privately owned, Margeson Lake is not regulated by the state and does not require permitting for its operation. The dam structure itself is of earth type with a buttress core, and has an uncontrolled spillway. With a low hazard potential and a moderate risk assessment rating, Margeson Lake provides a safe and enjoyable recreational environment for water resource and climate enthusiasts to explore and appreciate. Although its condition has not been rated, regular inspections have been conducted to ensure the safety of the dam and surrounding area.

Year Completed

1960

Dam Length

374

Dam Height

25

River Or Stream

SAWMILL BRANCH

Primary Dam Type

Earth

Surface Area

6

Nid Storage

73

Outlet Gates

Uncontrolled

Hazard Potential

Low

Foundations

Unlisted/Unknown

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.