Tolt Dam Early Warning System
This project will improve the resiliency and reliability of the Tolt Dam Early Warning System.
July 31, 2006 update
Project Substantially Complete
The replacement of the Tolt dam early warning system is complete. All indoor and outdoor sirens have been replaced with new sirens. SPU is working to finalize the contract documents within the coming months. The project is expected to be closed out by December, 2026.
Annual Siren Testing:
Starting in 2025, the frequency of audible testing of the sirens occurs once per year generally on the last Saturday in September. The annual test will continue to be coordinated in partnership with the City of Carnation.
Dam safety
The Tolt Dam has been and continues to be safe. The City of Seattle monitors the dam 24/7, 365 days a year with around-the-clock system operators and daily in-person safety checks at the site. Automated continuous monitoring of reservoir level, upstream and downstream river flows, and dam safety sensors are also a part of the 24/7/365 dam safety watch.
Tolt Dam Early Warning (Siren) System
The Tolt Dam is equipped with an Early Warning System intended to alert downstream residents in the City of Carnation and surrounding areas in the unlikely event of a dam emergency. The warning system has four indoor and seven outdoor sirens (see siren and annunciator locations on this page).
In the unlikely event of a Tolt Dam emergency, the City of Seattle will also promptly notify the King County Office of Emergency Management, City of Carnation and other emergency management agencies. In turn, they will provide public notifications using existing emergency notification systems including the Wireless Emergency Alert system, King County ALERT notifications, Reverse 911 phone calls, and weather radio notifications.
Under the State law (RCW 38.52), emergency management including alerting and evacuation of local residents for all pertinent hazards is the responsibility of local jurisdictions. The City of Carnation is responsible for emergency management within its incorporated limits while King County is responsible for the unincorporated areas.
The City of Seattle, as the owner and operator of the Tolt dam, is responsible for the safety of the dam and notifying emergency management agencies of any emergency related to the dam. The City of Seattle works closely with the City of Carnation and King County on emergency preparedness related to the Tolt Dam.
Third-Party review report
In 2024, the City of Seattle, with concurrence from the City of Carnation, voluntarily hired an independent panel of experts to review the Tolt Dam Early Warning (siren) System. The scope of this work included reviewing the following items:
- Tolt Dam Early Warning System and siren sounding incidents
- Dam safety assessments
- Emergency management roles and responsibilities, and public alerting
- Public communication
The panel included experts in dam safety, risk communication, emergency alerting and warning, and risk management. The panel was responsible for evaluating them with respect to current regulations and industry best practices and provide findings and recommendations for a path forward.
The panel has completed their review and prepared a full report, executive summary, and a statement about the July 4, 2025, Texas floods.
The updated Early Warning System includes seven outdoor sirens and four indoor sirens, also called annunciators, in Carnation. All of the original siren locations were replaced with new equipment, and three new outdoor locations were added.
- 35805 NE 80th St (replaced outdoor siren)
- 6921 Tolt River Rd NE (replaced outdoor siren)
- 5502 Tolt River Rd NE (replaced outdoor siren)
- 32421 E Entwistle St (replaced outdoor siren)
- Tolt MacDonald Park (new outdoor siren)
- Near the intersection of NE 60th St and SR 203 (new outdoor siren)
- Tolt Highlands Rd NE and Tolt River Road NE, City of Carnation Public Works yard (new outdoor siren)
- 4950 Tolt Ave –Elementary School (replaced indoor annunciator)
- 3740 Tolt Avenue –Middle School (replaced indoor annunciator)
- 3944 320th Ave NE – Bus Facility (replaced indoor annunciator)
- 3600 Tolt Ave – Fire Station (replaced indoor annunciator)
- Design: 2021
- Permits & Final Design: 2021-2022
- Construction & Commissioning: 2023-2026
- Project Completion: 2026
Seattle Public Utilities (SPU) owns and operates the Tolt Reservoir and Dams, located 16 miles upstream from the City of Carnation on the South Fork Tolt River. The reservoir stores 57,900 acre-ft of water to supply 30% of the drinking water for 1.6 million people in the greater Seattle area. Seattle City Light (SCL) owns and operates a system that generates power from water released from the South Fork Tolt Dam. Both SPU and SCL are bound to Federal Energy Regulatory Committee (FERC) requirements.
The Tolt Early Warning System alerts residents in the City of Carnation and in the nearby unincorporated area to evacuate in the unlikely event of a dam failure. The very first siren for the Tolt Dam area was implemented in 1978 as a single siren controlled by King County. The City of Seattle took over responsibility for the siren network in 1981 and the first improved network was installed in 1985. Additional improvements were made in 1993. The aging system, now in its fifth generation, was replaced with state-of-the-art equipment in 2026.