Mobile sinks (MS) mounted upon urban vehicles with fixed trajectories (e.g. buses) provide the ideal infrastructure to effectively retrieve sensory data from isolated Wireless Sensor Network (WSN) fields. Existing approaches involve either single-hop transfer of data from sensors that lie within the MS’s range or heavy involvement of network periphery nodes in data retrieval, processing, buffering and delivering tasks. These nodes run the risk of rapid energy exhaustion resulting in loss of network connectivity. Our proposed protocol aims at minimizing the overall network overhead and energy expenditure associated with the multi-hop data retrieval process while also ensuring balanced energy consumption among network nodes and prolonged network lifetime. This is achieved through building cluster structures consisted of member nodes that route their measured data to their assigned cluster head (CH). CHs perform data filtering upon raw data exploiting potential spatial-temporal data redundancy and forward the filtered information to appropriate end nodes.