Research on the role of local institutions in conflict management is still limited. This study highlights various inter-settlement conflicts over the issue of unclear resource boundaries in Danau Sentarum National Park, Indonesia. The park is home to two major ethnic groups (Dayak Iban and Malay) whose livelihoods are highly dependent on fish and forest resources available in the park area. We demonstrate how local institutions (adat) are used to address boundary conflicts and consider their effectiveness. The study also discusses challenges that adat face in ensuring the effectiveness of conflict management. We argue that enhancing communication and developing a mechanism of exchange among settlements engaged in conflict will promote better understanding of the problem and thus allows improvement in the current approaches in managing conflict. We propose a co-management arrangement to ensure the sustainability of the park and to constructively manage the conflict in the area.