This paper presents lightweight and flexible sensors for conductivity, temperature, and depth (CTD). CTD sensors are heavily used in oceanography to determine the salinity, which is a critical factor in the determination of mixingdensity, currents, weather and more. The graphene sensors are fabricated by laser printing on flexible polyimide. They combine corrosion resistance with a good conductivity and piezoresistivity in a robust platform, enabling the detection of conductance, temperature, and pressure. The performance of the graphene sensor was demonstrated in harsh environments with pressures up to 12 MPa and prolonged exposure to highly saline seawater. The printed sensors are durable and lightweight, making ideal for use as stationary monitory sensors or attached to a wide range of marine animals.