Serious games are increasingly used to facilitate stakeholder discussion and collaboration. Much attention is given in the game design literature on how to choose and design a serious game’s scope, content, mechanics, and link to reality in order to achieve the game’s intended learning outcomes. In this paper, we focus on how a serious game’s interface and the interaction it elicits contributes to achieving learning outcomes. We do so in the context of the Virtual River, a serious game focused on river management. Following the design and evaluation of a paper prototype of the Virtual River, a design challenge arose as the highly simplified models of reality used was perceived as a black box by non-expert participants, while expert participants perceived it as oversimplified and unrealistic. As hydrodynamic models used in river management practice are in itself perceived by non-experts as a black box, we decided to look for ways to simplify the interaction with such models in the game. Here, we present a tangible user interface for the Virtual River. The interface enables participants to get a better grip on the hydrodynamics of a river system. The system is set up as a discussion platform where the game board and its tangible game pieces help participants express their thoughts and ideas. We argue that using tangible interaction in Virtual River contributes to social learning outcomes by providing hypotheses based on literature and present how we intend to test these hypotheses.