This design guidance manual provides methods and criteria for assessing the retrofit potential of existing stormwater ponds, and selection and design guidance for stormwater pond retrofits that improve water quality treatment performance. The Kitsap County Public Works Department currently has responsibility for operation and maintenance of over 300 of the approximately 600 stormwater ponds in the County. Herrera worked with the County to conduct a study of these ponds to assess water quality retrofit potential and identify retrofit solutions, and ultimately developed conceptual designs to retrofit the highest-ranking ponds. The methods used to evaluate the County-owned ponds and identify preferred water quality retrofit solutions for those high-priority ponds are summarized in this manual and can be used as templates for other retrofit evaluations across the region.