A swimmer surveillance system configured to detect swimmers in a water body that are in a state of distress, or in a danger of drowning, and provide an alarm signal for prompting assistance to the swimmers in distress or in a danger of drowning, the system including: a processor; at least one swimmer sensor signally connected to the processor, and configured to attach to a swimmer, acquire data relating to an at least one physiological condition of the swimmer, and transmit the data to the processor; at least one image acquiring device signally connected to the processor, and configured to acquire images of the swimmers in the water body, and transmit visual data of the acquired images to the processor; and at least one alarming device signally connected to the processor, and configured to receive a signal from the processor and in response provide an alarm.