We aim to determine arsenic(III) in natural aquatic systems in the nanomolar range and at natural pH. In view of a future application of a gel integrated electrochemical detection approach to reduce fouling and to control mass transport, we introduce here a microelectrode capable of quantifying As(III) that consists of a gold plated Ir-based microelectrode (Au-IrM). The key advantage of this approach is the ability to renew the Au layer by electrochemical control for better robustness in the field. The microsensor was electrochemically characterized by Square Wave Anodic Stripping Voltammetry. The obtained results demonstrate that the stripping peaks exhibit reproducible linear calibration curves at pH 8 for As(III) concentrations from 10 to 50 nM and from 1 to 10 nM, using 3 and 36 min preconcentration times, respectively. The interference by copper and chloride is negligible for an As : Cu concentration ratio of 1 : 20 and a chloride concentration of 0.6 M typically found in seawater. The gold layer exhibits a lifetime of 7 days. The measurements are reproducible over time for a given gold layer (RSD < 9%) and between renewed layers (RSD ≤ 12.5%). While this work forms the basis for further progress on gel coated microelectrode arrays, As(III) detection in freshwater samples was successfully demonstrated here.