One of the main issues in wireless sensor networks (WSNs) is energy consumption. Normally, sensors are battery powered and in many applications it is impossible to recharge them. Proactive routing protocols are mainly used for data gathering in applications where the sink needs to collect data periodically. On the other hand, for sparse or event-based data reporting, reactive routing protocols are preferred. In this way the routing information is not maintained up to date if no data are reported. Thus no energy is wasted on maintaining paths in the periods of inactivity. In this paper we propose an innovative reactive routing protocol using eventbased clustering for composite event reporting. To avoid frequent updating of the delivery paths, we use anchor nodes that act as relays between the convergecast tree and the mobile sink. We analyze the performance of our algorithm using WSNet simulator, which is specially designed for event based applications in WSNs. We compare the performance of our reactive protocol with its proactive version.