We identified Ecological Systems of Concern (ESOC) based on the conservation status rank of each ecological system. Each ESOC is described within the formation overview and specific stressors and actions are highlighted, as well as the SGCN associated with that system. The Washington Natural Heritage Program assigned conservation status ranks to Washington’s ecological systems using NatureServe’s Conservation Status Rank calculator. The Conservation Status Rank is a measure of an ecological system’s elimination risk. The rank is calculated using a measure of eight core factors relevant to risk assessment of elimination. The factors are organized into three categories: rarity, threats, and trends. Factors are scaled and weighted and subsequently scored according to their impact on risk. WDFW identified systems with S1, S1S2, and S2 ranks as Ecological Systems of Concern.