Abstract: The document relates to a sensor arrangement for underwater detection of a leak in fluid carrying body, comprising a sensor support structure mountable to a carrier for enabling the sensor support structure to be suitably positioned or moved. A plurality of thermal sensors is distributed on the sensor support structure forming a sensor array. The sensors are provided by optical fibers connectable to an interrogator via optical signal connectors. Each fiber comprises intrinsic fiber optic sensors at respective locations within the fiber, forming the thermal sensors. The fibers are arranged on the support structure such that the intrinsic fiber optic sensors is distributed across the support structure to span a detection area. The document further relates to a method of performing leak detection as well as for discovering natural occurring leaks (sources).