An experimental study has been performed to investigate the effects of sustained hydrostatic depth pressure saltwater immersion coupled with low temperatures on the mechanical and structural integrity properties of additively manufactured (AM) polymer and resin-based materials. The materials that were evaluated in the study were produced by both the material extrusion and Vat Photopolymerization printing methods. The material extrusion materials consisted of Stratasys ULTEM 9085 and Markforged Onyx, and the Vat Photopolymerization material was Accura ClearVue resin. Water immersion was conducted with 3.5% NaCl solution at room temperature under a pressure of 34.5 MPa (5000 lb/in2) in a novel test facility for long-duration, high-pressure water saturation. Each material was characterized in two conditions: (1) baseline with no water saturation and (2) 60-day water immersion. Furthermore, each material was tested in the dry and saturated conditions at temperatures of 20 °C, 0 °C, and − 20 °C. The change in mechanical properties as a function of saltwater exposure and temperature was quantified through tension, compression, flexure, and in-plane fracture toughness in controlled laboratory testing. Additionally, non-destructive testing in the form of SEM Microscopy and TeraHertz imaging scans was conducted to analyze the physical material changes through the thickness of the material due to the saline water absorption. The significant findings of the study highlight that both saltwater immersion and low temperature have differing effects on additively manufactured materials based on the material composition of the base material, and thus significant consideration must be given to material selection in marine environments.