Public participation in water quality planning for upper Narragansett Bay, Rhode Island (RI), has changed from hearings to a stakeholder approach. As a result of this innovation in process, knowledge about environmental science and about citizen preferences is more widely shared. High levels of stakeholder motivation to contrib± ute, as evidenced by meeting attendance and participation, developed from this new distribution of power and knowledge. Synergisms among process, knowledge, and motivation contributed to a much more acceptable plan for enhancing water quality. In Narragansett Bay the solution adopted to improve water quality was to store and treat combined sewer over ows (CSOs). T his stakeholders' plan requires a 2± year period of monitoring after the initial phase of building the system. Sub± sequent construction will complete the project as originally planned or revise it in an adaptive manner if more e ective solutions than were originally envisioned become available.Public participation is growing and transforming environmenta l decision processes. M any citizens desire to move from providing external reviews of agency plans to direct involvement in identifying and evaluatin g options. This article examines the nature and implications of these changes for water quality planning. I consider relationships among public participation process, knowledge, and motivation that collectively in uence outcome.In upper Narragansett Bay, Rhode Island (RI), two water quality plans have been completed with signi cantly diOEerent styles of public participation. Both plans are directed to combined sewer over ows (CSOs). CSOs originate because street drains collect precipitation and combine it with normal sewerage. During wet periods, the combined ow can exceed sewage treatment plant capacity so it is shunted to the estuary through a CSO pipe. The untreated effluent contains a variety of pollutants that are associated with low water quality.This article contrasts the two decision processes and contents of the plans pro± duced. This serendipitous experiment in diOEerent modes of public participation occurred because two plans were produced for the same problem on the bay. The I thank the stakeholders and the staOE of NBC who allowed access to the process and three anonymous reviewers for many helpful comments.