This paper, prepared with the framework of the "Building Inclusive Urban Communities" / BInUCom project (funded under EU Erasmus plus program) attempts to examine the link between occupational change and transformation of land tenure in a Koliwada (urban fishing village) in Mumbai. Koliwadas are heterogeneous settlements, with mixed ethnicities and livelihoods, diverse physical settings and conditions and varied systems of land tenure and customary rights. This paper argues that behind the aggressive mobilization of ethnic identities and consequent conflicts between communities in urban fishing villages lie conflicting claims over the control and use of urban land. It argues that binaries adopted by planning and development discourse such as formal / informal, authorized / unauthorized, indigenous / migrant, and Koliwada / slum are inadequate to understand the complex intra and inter-community dynamics of these hybrid and accretive settlements. This case study highlights micro-spatial transformations, where a decline in the primary occupation of fishing are behind the attempts of ethnic fishers to commodify the traditional commons – with the expectation of gains through changes in land use and displacement of traditional rights to land.