Sensing apparatus (24) includes one or more sensors (26, 28, 46, 48), configured to sense properties of water in which the sensing apparatus floats. A wireless communication interface (42) is coupled to transmit signals indicative of an output of the one or more sensors. An energy storage device (58) is coupled to provide electrical energy to the one or more sensors and to the wireless communication interface. A sealed case (25) contains the one or more sensors, the wireless communication interface, and the energy storage device and has sufficient buoyancy to float in the water.
