In 1928, when the Bureau for the Project of Amelioration of Polesie (a large marshy area in the eastern part of interwar Poland) began its field studies, environmental concerns were low on the list of its priorities. A year later, this brought the Bureau into serious conflict with the State Council for Nature Protection. When both institutions eventually came to terms with their contradictory ambitions and vaguely-defined competences to enter into substantial cooperation, the idea of reserving a large area of marshlands as a natural park came into being. In 1932, Stanisław Kulczyński, a botanist leading the Bureau’s peat bog research team and also a Council member, proposed protecting an area of roughly 100,000 hectares between the Lwa and Stwiga rivers. The future park would encompass most types of landscape typical of Polesie and, fortunately, most of its swamps, forests, dunes, and peat bogs were barely touched by human activity. The hydrogeological feature of the selected area safeguarded its immunity to the potential consequences of the amelioration works, if such were undertaken in any of the surrounding areas. This paper explores how the location and extent of the protection of the park were negotiated within the entangled networks of social, economic, and political agendas of national policy in inter-war Poland. The efforts to coordinate the pro-nature policy in Polesie with similar actions undertaken by the Soviets beyond the nearby border are also covered.