Lake Sylvia State Park closed, dam under active monitoring

MONTESANO – Lake Sylvia State Park is closed while crews respond to impacts brought on by this week’s heavy rain. 

The current atmospheric river weather event has raised lake levels and placed added stress on the Lake Sylvia dam. For public safety, the park and all trail systems leading into and around the park and dam are closed until further notice. 

For the safety of visitors and residents: 

• Downstream residents in the Sylvia Creek area should be prepared for additional flooding and remain ready to take action on short notice 
• Residents should avoid all trails leading toward Lake Sylvia 
• Additional alerts will be issued if conditions change 

Elevated water levels and continued rainfall are creating concerns about the pressure placed on the 100-year-old dam.  

Crews are continuously monitoring the dam and at this time there are no visual structural changes. Water levels have receded by approximately one foot since Monday evening.  

State Parks staff are actively on site conducting safety and mitigation work, including: 

• Regional maintenance and arbor crews responding to a mudslide at the park entrance 
• Marine crews clearing logs and debris to improve water outflow and clearing dam spillways to allow increased water release 
• Safety staff assessing monitoring systems and providing water-level data 

Monitoring and response efforts are being closely coordinated between State Parks and local emergency management partners, including the Washington State Department of Ecology, City of Montesano and Grays Harbor County.  

An official inspection of the dam to assess the impact of this event will occur after the weather clears, once conditions allow. 

More heavy rain is forecast in the coming days, which may cause lake levels to rise again.  

Background 

Lake Sylvia State Park is located on Sylvia Creek, about four miles upstream of its confluence with the Wynoochee River. The current concrete buttress dam was built by Puget Sound Power and Light in 1918. Portions of the structure were reinforced between 1988 and 1995.  

In 2025, during the dam’s most recent annual inspection, crews identified structural concerns due to the age and construction of the dam. In response, in June, State Parks lowered the level of Lake Sylvia by approximately five feet, down to the height of the reinforced section of the dam. Additionally, State Parks installed an electronic monitoring system and implemented safety protocols for high-water events. State Parks is currently in the process of developing a scope of work to further assess the dam and identify long-term solutions.  

This temporary reduction relieves pressure on the structure while State Parks and its partners closely monitor its condition and begin planning for long-term improvements to address the aging dam.