Buying a House Near a Stream or Wetland in Snohomish or King County (2026)

Short answer: A creek, pond or wetland can make a lot feel special, but it also comes with a protective buffer where building, clearing and grading are limited. In unincorporated Snohomish County, stream buffers run 50 to 150 feet and wetland buffers 40 to 225 feet or more, measured from the water’s edge or the wetland boundary. Before you buy, find out what’s on or near the lot, how wide the buffers are, and whether anything you plan to build fits outside them.

This is general information, not legal, environmental or permitting advice. Each city and county has its own critical areas code, and buffers depend on a professional’s rating of the specific stream or wetland. Confirm with the permitting office before you rely on any number here.

Why streams and wetlands come with rules

Washington’s Growth Management Act lists wetlands, fish and wildlife habitat conservation areas, frequently flooded areas, geologically hazardous areas and aquifer recharge areas as "critical areas" (RCW 36.70A.030), and requires every county and city to adopt development regulations that protect them (RCW 36.70A.060). The Department of Ecology, the state’s lead wetland regulatory agency, says that under the Growth Management Act local governments designate and protect wetlands by adopting critical areas ordinances. At the federal level, the U.S. Army Corps of Engineers administers Section 404 of the Clean Water Act.

Larger waters add another layer. Under the Shoreline Management Act, "shorelands" extend 200 feet landward from the ordinary high water mark of shorelines of the state, which generally include lakes of 20 acres or more and streams with a mean annual flow above 20 cubic feet per second (RCW 90.58.030). Those areas fall under a local shoreline master program as well.

How wide the buffers are in Snohomish County

For unincorporated Snohomish County, buffer widths are set in SCC 30.62A.320. Here are the standard widths for streams and a selection of wetland types.

Based on: Snohomish County Code 30.62A.320, Tables 2a and 2b (standard buffer column; high- and low-intensity uses have different widths). Unincorporated Snohomish County only.

A few rules in the same section can make the buffer wider than the table suggests. Stream buffers are measured from the ordinary high-water mark, or from the edge of a mapped channel migration zone. Wetland buffers are measured from the wetland edge. If the buffer reaches a slope of 33 percent or more, it extends to 25 feet beyond the top of the slope. In a special flood hazard area, the buffer is the greater of the table width, the channel migration zone plus 50 feet, or the mapped floodway. And where two buffers overlap, the wider one applies.

Snohomish County’s Critical Area Requirements page adds that a buffer from a stream or wetland on a neighboring lot can extend onto the property you’re looking at, and that residential projects within 400 feet of geologic hazards or 500 feet of other critical areas must identify them.

What building near a buffer involves

Snohomish County’s Assistance Bulletin #15, revised September 2025, says you can usually develop in or near critical areas if there’s no other location on the lot, disruption is minimized and mitigation is provided. When wetlands or fish and wildlife habitat are on the lot or within 300 feet of the project, expect buffers, a mitigation plan, possibly a habitat management plan, and a critical area protection area recorded with the County Auditor. A critical area study is generally required, and a Critical Area Site Plan is recorded before the permit is issued. Lots created before October 1, 2007 may qualify for some exceptions.

In King County, the updated critical areas ordinance was adopted December 2, 2025 and took effect February 18, 2026 (except in shoreline jurisdiction). Projects that encroach into a stream, wetland or buffer need a critical area mitigation plan; small projects with less than 1,000 square feet of buffer impact can typically use the county’s Restoration and Enhancement Guidelines. If critical areas would deny all reasonable use of a lot, a reasonable use exception may apply.

Work in or near the water itself is a state matter too. The Department of Fish and Wildlife requires a Hydraulic Project Approval before hydraulic projects in or near state waters, which includes most marine and fresh waters. Snohomish County’s bulletin adds that work in or near water may also need permits from the U.S. Army Corps of Engineers or Ecology.

What to check before you buy

Based on: RCW 64.06.020 (Form 17 Items 7A and 7D); Snohomish County Assistance Bulletin #15 and Streams pages; King County Critical Areas page, Critical Areas Designation handout and Wetlands page. Cities set their own rules.

RCW 64.06.020 currently has two versions on the Legislature’s site: one marked effective until January 1, 2027, and one effective January 1, 2027. The questions quoted here appear in both. If your sale runs across the new year, check which form is being used. If you plan to add an ADU, a shop or a bigger driveway, ask before your inspection deadline whether it fits outside the buffers; our guide to contingencies explains how those deadlines work. Water on a lot often comes with other questions, so see our guides to buying in a flood zone, buying a house on a slope and buying a home with a septic system or private well, since buffers can limit where a drainfield or well goes.

FAQ

How big is a stream or wetland buffer in Snohomish County?

In unincorporated Snohomish County, SCC 30.62A.320 sets standard buffers of 150 feet for Type S and Type F streams and 50 feet for Type Np and Ns streams. Standard wetland buffers run from 40 feet for a Category IV wetland up to 225 feet for wetlands with high habitat function, and wetlands containing salmonids get at least 150 feet. Cities in the county have their own codes.

Can I build an addition or ADU near a wetland?

Sometimes. Snohomish County’s Assistance Bulletin #15 says you can usually develop in or near critical areas if there’s no other location on the lot, disruption is minimized and mitigation is provided. That usually means a critical area study and a recorded site plan. In King County, encroaching into a stream, wetland or buffer requires a critical area mitigation plan.

How do I find out if a property has a wetland before I buy?

Read Form 17 Item 7D, which asks about shorelines, wetlands, floodplains or critical areas. In King County you can apply for a Critical Areas Designation, which is valid for five years and can be used in real estate transactions. In Snohomish County, a pre-application meeting with Planning and Development Services is a starting point. Both counties publish critical area maps.

Does the seller have to disclose a stream or wetland?

Form 17 asks, "Are there any shorelines, wetlands, floodplains, or critical areas on the property?" Answers are based on the seller’s actual knowledge, and a seller may honestly not know. Buffers from a stream or wetland on a neighbor’s lot can also reach onto the property, so don’t rely only on the form.

Do I need a state permit to work near a creek?

Often. Washington’s Department of Fish and Wildlife says people planning hydraulic projects in or near state waters, which includes most marine and fresh waters, need a Hydraulic Project Approval before starting work. Snohomish County notes that work in or near water may also need Army Corps of Engineers or Ecology permits.

Talk it through with a local agent

Peter Kim and Odigo Real Estate Club can help you spot critical area questions early and line up the right calls to the county before you’re committed, with 25+ years combined experience, 593+ closings, and 122 five-star Zillow reviews. See our home buying services.

Odigo Real Estate Club · REAL Brokerage, WA #112064 · 16108 Ash Way, Suite 201, Lynnwood, WA 98087 · (425) 409-3823 · Mon–Sat 9 AM–6 PM, closed Sunday

Sources

• Snohomish County Code, SCC 30.62A.320, Stream, lake, and marine buffers and wetland buffer width standards (Tables 2a and 2b; measurement rules; 33 percent slopes; overlapping buffers), https://snohomish.county.codes/SCC/30.62A.320 , accessed Nov 3, 2026.
• Snohomish County Planning and Development Services, Assistance Bulletin #15, Critical Areas Regulations for Residential Projects (PDF, revised September 2025) (studies, mitigation, recorded site plans, pre-application fee, lots created before October 1, 2007), https://www.snohomishcountywa.gov/DocumentCenter/View/8064/15---Critical-Areas-Regulations-for-Residential-Projects-PDF?bidId= , accessed Nov 3, 2026.
• Snohomish County, Critical Area Requirements (400-foot and 500-foot identification distances; off-site buffers), https://www.snohomishcountywa.gov/2925/Critical-Area-Requirements , accessed Nov 3, 2026.
• Snohomish County Surface Water Management, Streamside Landowner Program (technical help, free site visits, free native trees and shrubs), https://www.snohomishcountywa.gov/862/Streams , accessed Nov 3, 2026.
• King County Department of Local Services, Critical areas (CAO adopted December 2, 2025, effective February 18, 2026; mitigation plans; 1,000 square feet; reasonable use exception; CAD), https://kingcounty.gov/en/dept/local-services/certificates-permits-licenses/permits/permits-inspections-codes-buildings-land-use/permit-forms-application-materials/land-use/critical-areas , accessed Nov 3, 2026.
• King County Department of Local Services, Critical Areas Designation handout (valid five years; use in real estate transactions), https://kingcounty.gov/en/-/media/king-county/depts/local-services/permits/land-use/critical-areas-designation-handout.ashx , accessed Nov 3, 2026.
• King County Department of Natural Resources and Parks, Wetlands (KCC 21A.24; sensitive area notices on property titles; map layer), https://kingcounty.gov/en/dept/dnrp/nature-recreation/environment-ecology-conservation/wetlands , accessed Nov 3, 2026.
• Washington State Department of Ecology, Wetlands (lead state wetland regulatory agency), https://ecology.wa.gov/water-shorelines/wetlands , accessed Nov 3, 2026.
• Washington State Department of Ecology, Wetland regulations (Growth Management Act and critical areas ordinances; Corps and Clean Water Act Section 404), https://ecology.wa.gov/water-shorelines/wetlands/regulations , accessed Nov 3, 2026.
• Washington Department of Fish and Wildlife, Hydraulic Project Approval (HPA) (HPA required for hydraulic projects in or near state waters), https://wdfw.wa.gov/licenses/environmental/hpa , accessed Nov 3, 2026.
• Washington State Legislature, RCW 36.70A.030 (Growth Management Act definitions, including critical areas), https://app.leg.wa.gov/RCW/default.aspx?cite=36.70A.030 , accessed Nov 3, 2026.
• Washington State Legislature, RCW 36.70A.060 (development regulations that protect critical areas), https://app.leg.wa.gov/RCW/default.aspx?cite=36.70A.060 , accessed Nov 3, 2026.
• Washington State Legislature, RCW 90.58.030 (Shoreline Management Act definitions; shorelands 200 feet; 20 acres; 20 cubic feet per second), https://app.leg.wa.gov/RCW/default.aspx?cite=90.58.030 , accessed Nov 3, 2026.
• Washington State Legislature, RCW 64.06.020 (seller disclosure statement form; version effective until Jan 1, 2027 and version effective Jan 1, 2027), https://app.leg.wa.gov/RCW/default.aspx?cite=64.06.020 , accessed Nov 3, 2026.

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