Environmental & Ecological Services

---

Wetlands go by many names: bogs, marshes, swamps, ponds, prairie potholes, sloughs, fens, wet meadows, bottomlands and more. While some wetlands like swamps and marshes are easy to recognize, many are not. Some are dry for part of the year, and others simply do not appear wet at first glance. Wetlands are generally defined as areas covered by water or with waterlogged soils for extended periods during the growing season, supporting plant communities specifically adapted to survive in saturated soil conditions. The U.S. Army Corps of Engineers and the U.S. Environmental Protection Agency define wetlands as:

"Those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions."

The key takeaway: not all wetlands look the same, not all wetlands are visibly wet, and not all wet areas qualify as wetlands.

A wetland delineation is a field study that identifies the precise boundaries of a wetland. Delineations must be performed in accordance with the 1987 Corps of Engineers Wetland Delineation Manual and the applicable Regional Supplement for your geographic area. A qualified wetland scientist conducts the field investigation and prepares a delineation report that meets U.S. Army Corps of Engineers (Corps) requirements.

The delineation establishes both the location and physical extent of a wetland for purposes of federal, state, and local regulation. It also serves as a foundational element of a Jurisdictional Determination (JD), which identifies which water bodies within a project area meet the legal definition of "Waters of the United States" (WOTUS) under the Clean Water Act.

The regulatory landscape governing jurisdictional determinations has evolved significantly in recent years. The U.S. Supreme Court's 2023 decision in Sackett v. Environmental Protection Agency substantially narrowed the definition of WOTUS, and federal agencies have continued to issue updated guidance in response, most recently in March 2025. The current definition of WOTUS also varies by state due to ongoing litigation. CES stays current with these regulatory developments to ensure every delineation and jurisdictional determination we prepare reflects the most up-to-date requirements.

For additional information on jurisdictional determinations, refer to Corps Regulatory Guidance Letter 16-01.

Most cities and counties in Washington State require the use of the Washington State Department of Ecology Wetland Rating System to classify wetlands. There are two rating system manuals: one for Western Washington and one for Eastern Washington (east of the Cascade Range). The most current version, Version 2 of the 2014 Rating System, was released in July 2023 and reflects the latest available science.

The rating system evaluates each wetland by type - depressional, riverine, lake-fringe, or slope - and assigns it a category from 1 to 4. A Category 1 wetland represents the highest quality and most sensitive wetland, while a Category 4 represents the lowest quality. These ratings directly inform the buffer standards and regulatory requirements that apply to each wetland under local critical areas ordinances.