Surprises - large, unexpected changes from apparently small causes -- are common in systems of people and nature. Are these surprises a consequence of the complexity or nonlinearity of natural-social systems? Or can they be explained by simpler processes? Our research addresses this question for systems composed of lakes, their shoreline (riparian) vegetation and land use, and social and economic organizations of lake users. We will study the self-organization of lake users and associated characteristics of shoreline and lake ecosystems. We will determine whether thresholds in riparian organization set the stage for an important class of surprises - collapses of economically important game fish stocks. We will test the possibility that nonlinear dynamics can be used to design manipulations that remove invading crayfish from a lake. If successful, our experiment will cause a self-sustaining removal of an invasive species - a path-breaking ecological restoration.