Oxia Planum, the landing site for the ExoMars rover mission, is a shallow basin on the southern margin of Chryse Planitia that hosts remnants of sediment fans associated with the ancient channel system Coogoon Vallis. This indicates runoff from a catchment in Arabia Terra has transported material into the landing site. To explore this fluvial system we created a model catchment for Oxia Planum and, using 6 m/pixel ConTeXt camera (CTX) orbital remote sensing image data, we digitised the fluvial and lacustrine landforms in Western Arabia Terra in and around this catchment. We find: (1) The catchment has a minimum area of ~2.1×10⁵ km² and has been episodically deformed by tectonic activity; (2) There were at least two phases of fluvial activity. The first created a mature landscape associated with Coogoon Vallis, which may have deposited alluvial or deltaic deposits in the Oxia Basin. After a substantial hiatus, a second phase of activity incised u-section channels into the pre-existing landscape and channel systems; and (3) Evidence for numerous possible paleolake deposits within the catchment. These are not well connected to the fluvial system and were probably sustained by ground water activity contemporaneous with both phases of fluvial activity. This groundwater might have modified the geochemistry of Oxia Planum. Oxia Planum probably experienced an alluvial or distal deltaic/lacustrine depositional environment during the mid Noachian, which was later overprinted by a younger phase of fluvial activity.