Lake Sylvia sits in a wooded draw about three miles north of Montesano in Grays Harbor County, close enough to US 12 that you can be in the water not long after leaving the highway. The lake is not natural. It is a millpond on Sylvia Creek, four miles upstream of where that creek meets the Wynoochee River, and the water is held back by a concrete buttress dam that Puget Sound Power and Light finished in 1918. That dam raised the lake sixteen feet and pushed it farther up the valley. Before the dam there was a sawmill here, the first in Grays Harbor County, cutting lumber from 1871. The City of Montesano bought the logged watershed in 1931 for $12,000 to protect its drinking water, then deeded 234 acres around the lake to the State Parks Committee on 23 October 1936. The park today covers 233 acres of dense temperate rain forest.

Swimming is in the day use area toward the south end of the lake, a short walk from a small asphalt lot near the dam. This is the part that has changed, and it is worth knowing before you drive out. A Washington Department of Ecology dam safety inspection in November 2024 reported back to State Parks in March 2025 and found the 1918 structure at Emergency Level 1 at its normal water height. State Parks responded by lowering the lake roughly five feet, down to the height of the section reinforced between 1988 and 1995. That drop took the dam off Emergency Level 1, and it is where the lake has stayed. For swimmers the practical effect is that the old roped swim zone is now dry sand. There is more beach than there used to be, and State Parks asks people to watch their footing around logs and stumps that the lower water has uncovered along the new shoreline.

The park stays open for swimming, paddling and fishing through all of this, with hours of 8 a.m. to dusk year round. Heavy rain in December 2025 briefly closed the park and its trails while crews monitored the dam during an atmospheric river, so it is worth checking the park alert page after a big storm, though no closure is standing now.

Parking requires a Discover Pass, a Washington State government fee rather than anything the park sets on its own. It runs $45 for the year or $10 for a single day. The state designates twelve free parking days in 2026: 1 January, 19 January, 9 March, 19 March, 22 April, 6 and 7 June, 19 June, 9 August, 26 September, 10 October and 11 November. Free days cover parking only, not overnight stays or rented facilities.

Camping is on site, with 31 standard sites, four walk-in, two hiker and biker sites, three partial hookup sites and a group camp, reservable from 1 April through 30 September, with showers and a dump station. Five miles of hiking and biking trail include a loop around the lake, alongside a half mile of ADA trail. Anglers fish from the bridge, and the lake is stocked in season, so a Washington recreational fishing licence applies. Since August 2025 the boat launch has been closed to trailered boats, but a kayak, canoe or paddleboard you can carry may still be hand launched, and the park store no longer rents them.