This work presents the development, characterization and field validation of newly designed gel-integrated nanostructured gold-basedmicroelectrode arrays (Au-GIMEs) enabling the direct detection of inorganic arsenite (As(III)) in fresh and marine aquatic systems. They consist of renewable Au nanoparticles (AuNP) or Au nanofilaments (AuNF) electroplated on 100- to 500- interconnected iridium (Ir)-based microdisk arrays and covered with a gel. The gel protects the sensor surface from fouling and ensures that mass transport of analytes toward the sensor surface is by diffusion only, and therefore independent of the ill-controlled hydrodynamic conditions of the media. The responses of these sensors to direct Square Wave Anodic Stripping Voltammetry (SWASV) quantification of As(III) at pH 7.6 were investigated first in 0.1 M NaNO3, then in fresh and marine water samples. The analytical responses were found to be correlated to the number of interconnected microelectrodes and the morphology of the nanostructured Au deposits but independent of the media composition. The new interconnected AuNF-GIME have sub-nanomolar detection and quantification limits fulfilling the requirement for direct monitoring of As(III) in fresh and marine aquatic systems. The AuNF-GIME were incorporated in a submersible multi-channel trace metal sensing probe for remote high-resolution monitoring. Field evaluation and validation was performed during a one-week field study in the Elbe Estuary (North Germany), from which environmental data are presented.