This article examines mudlarking, the practice of searching urban and coastal foreshores for historical objects, as a form of participatory archaeology that reveals how material, temporal, and social boundaries are continually negotiated. Using the concept of liminality as a theoretical lens, this article explores how mudlarking unsettles distinctions between land and water, past and present, and formal and informal knowledge, generating new ways of engaging with heritage in Aotearoa New Zealand and abroad. Drawing on material culture theory, this article demonstrates how found objects serve as sites of social construction, where value and meaning shift through interpretation and context. By situating mudlarking within global and local frameworks of heritage governance, this article highlights tensions between protection, participation, and authority. Through comparative discussion of practices and policies—from the Portable Antiquities Scheme in England and Wales to heritage legislation in Aotearoa New Zealand—it is argued that mudlarking exemplifies a radical encounter between archaeology, community, and environment. This study reveals how everyday engagements with the material past can transform understandings of heritage and invite more inclusive, adaptive, and relational modes of environmental knowledge-making.