In 2014, King County and the City of Seattle launched an effort to develop strategies to improve environmental conditions in the Green Duwamish Watershed. This initiative is meant to increase coordination of work in the watershed to better manage habitat restoration, salmon recovery, flood control, stormwater management, public health, social equity, environmental cleanups, economic development, open space preservation and water quality. The outcome from this phase identified regional stormwater management as a key to improving the health of the watershed. In 2016, a collective of experts in the watershed developed a strategy for the regional management of stormwater. A yearlong dialogue culminated in defining a purpose, vision, goals, objectives and strategies of a watershed wide program. This effort has now entered a transitional phase, pivoting from ‘planning’ to ‘doing’. In Washington State, NPDES permits have been evolving to include more watershed based planning. This presentation will share King County’s experience in facilitating partnerships, co-designing approaches to collaborative stormwater management programs, and enabling coordination across the landscape.