Wireless sensor networks have emerged as a fast-growing technology that has enabled us to monitor physical and environmental states. As of yet these valuable sensor networks have been bound to terrestrial terrains; however, seventy percent of the Earth's surface is covered by enormous bodies of water: oceans, seas and rivers. Most of this territory remains unchartered, and this primarily gave a rise to the implementation of these sensor networks underwater. In this paper, we present a new technique for localizing an event of interest in an underwater environment monitored by an underwater sensor network. We reduce the localization problem to the problem of finding 4-Node Coverage, in which we form a subset of nodes such that every node in the original set is covered by four nodes belonging to this special subset. Whenever a node detects an event, it is reactively localized using the anchor nodes, and the sink is supplied with the necessary information.