In this article, we bridge and extend concepts from behavioral game theory and the Ecology of Games Theory of Polycentricity (EGT) to test possible mechanisms for conflict contagion across the array of actors and policy forums that constitute a polycentric governance system. We argue that actors who experience conflict in one forum will develop about strategies in other forums, which then impacts the level of conflict exhibited in within-forum interactions. This behavioral spillover of conflict is a different mechanism than conflict that might be experienced when two forums are addressing the same policy issue(s), which may be characterized by higher or lower levels of conflict. We use survey data collected in the Tampa Bay (FL) and California Delta (CA) water governance systems to examine conflict contagion across forums. Using a series of spatial autoregressive models, we find evidence that co-membership networks serve as a conduit for conflict contagion among forums. Our results show that forum deliberations can be strongly impacted by interactions from other institutions and processes. Consistent with the idea of path dependence, “new” forums are not necessarily independent of the forums they replace, but rather, pre-existing levels of conflict and cooperation may constrain available outcomes.