Whatcom County, WA Environmental Rules: Erosion Control (2026)

410 governs seasonal clearing activity limitations for the unincorporated county, covering Birch Bay, Point Roberts, and rural areas outside Bellingham, Ferndale, Lynden, Blaine, Everson, Nooksack, and Sumas. County review and approval is required for all clearing activity tied to a fill and grade permit, building permit, or other development proposal. Clearing activity or forest practices that disturb more than 500 square feet of land are prohibited from October 1st through May 31st. 16 or Title 23; emergencies presenting an imminent threat to public health, safety, or the environment (with notice to the director within two business days); agricultural activity outside critical areas; and non-conversion forest practices regulated by the Washington Department of Natural Resources.

Even an exempt project must minimize soil disturbance to the maximum extent practicable, and the director can condition the exemption to require temporary erosion and sediment control. Within the Lake Whatcom Watershed Overlay District the restriction is stricter: any permit authorizing more than 500 square feet of disturbance must bar the work from September 15th through May 31st. Overlay district projects must install and have inspected temporary erosion and sediment control, such as silt fencing, check dams, covered excavation piles, and mulching, before any clearing begins, per the Whatcom County Development Standards, and the director conducts periodic inspections.

The director may require a phased clearing plan with a detailed schedule where slopes or proximity to shorelines and wetlands warrant it. All disturbed areas in the overlay district must receive soil stabilization within two days of disturbance unless a tree canopy retention plan provides equal or greater runoff protection.