This article presents a custom-made device designed to monitor water levels in salt marshes. The device is autonomous and embeds a distance sensor to periodically send measurements of water height to a base station using an Ultra High Frequency (UHF) radio link. These are then collected, processed and displayed to salt workers to help them to supervize the salt marshes productivity. An experimental deployement is carried out in the Guérande salt marshes (near the city of Nantes, France). Preliminary results clearly show the water evaporation inside the basin at the end of the afternoon. The device can be easily extended to numerous sensors in order to monitor several sites simultaneously and to control the water entrance through the hatch. More than a technical depiction, this paper describes the requirements of an ancestral task where a simple cyber physical system (CPS) can efficiently assist humans in their daily activity.