Heavy Metals are of environmental interest due to persistence in both fresh and marine water environments 1. Heavy metals in seawater come from both natural process and anthropogenic activities. 2. The main sources of anthropogenic pollution by heavy metals in the coastal regions include industrial wastes, liquid effluents and paint degradation of ships 3. Metal ions such as copper, zinc and cadmium at low concentrations are necessary micronutrients, however at higher concentration they become toxic for the aquatic ecosystems. It is therefore important to monitor such metals continuously. Herein we present a low cost autonomous sensing platform for the in-situ determination of cadmium, copper and lead in marine waters. The sensor was developed under the COMMONSENSE FP7 project (614155) and has been field tested at sites of environmental importance.