Tolt Dam Early Warning System

This project will improve the resiliency and reliability of the Tolt Dam Early Warning System.

December 3, 2025  update 

2025 Annual Siren Test Complete

On November 1, 2025, Seattle Public Utilities (SPU) successfully completed the annual test of the Tolt Dam Early Warning System, including the audible siren test messages in and near Carnation, WA. The SPU’s test was completed in coordination with the City of Carnation’s Be Dam Ready Event and Evacuation Drill.

City of Seattle staff, along with partners from King County Office of Emergency Management participated in the public event held at Tolt Middle School. Information about the Tolt Dam was shared with attendees and City of Carnation officials in a presentation by SPU.

Annual Siren Testing:

The frequency of audible testing of the sirens will now occur once a year, there will no longer be weekly Wednesday noon tests. The date of the annual test will be coordinated with the City of Carnation. (Typically, this happens the last Saturday of September during Carnation’s “Be Dam Ready” evacuation drill.) 

Moving to an annual test aligns with a recommendation from the third party report, providing an opportunity for system testing while minimizing unnecessary disruption for the community.

Those interested in the status of the siren system, including the siren testing, can stay updated by checking this website, subscribing to the project email distribution list or contacting the project team at tews.info@seattle.gov or (206) 684-5428. 

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. 

In 2020, the City of Seattle began a project to replace the aging early warning system with state-of-the-art technology and equipment that will improve the resiliency, reliability, and security of the system.

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.