Mud-dominated sediments in Presque Isle Bay are contaminated with metals and hydrocarbons derived from developed watershed and atmospheric sources. Prior to this study, the quantities, rates, and spatial distribution of long-term sedimentation and erosion in the bay were largely unknown. As a result, the fate of contaminated bay-floor sediments and possible rates of natural recovery for this Area of Concern (AOC) could not be determined. To provide baseline data useful to state and federal agencies monitoring recovery of the bay, this paper identifies: (1) the quantities, rates and patterns of 20^th Century sedimentation and erosion, (2) the major sediment inputs and outputs for the bay, and (3) the implications of the sedimentary regime on possible future rates of bay recovery. Bathymetric and sedimentological data show that 20^th Century net accumulation totaled approximately 3.94 ×10⁶ m³ which is equivalent to a dry sediment loading of 5.92 ×10⁹ kg (5.92 ×10⁶ t), or 6.29 kg/m²/yr (1.28 lb/ft²/yr) when averaged over the accretional 70% of the bay. This external loading represents approximately 50% of total accretion because externally derived sediments are augmented with resuspended sediments from shallow-water parts of the bay. The principal sediment inputs were littoral drift from ephemeral and permanent inlets (∼42%), artificial infilling along the shoreline (∼28%), streams (∼16%), bank/bluff erosion (∼12%), and biological production (∼2%). Dredging was the principal output. Based on long-term average sedimentation rates and patterns, recovery of the AOC through natural sediment capping will take at least several decades if source contaminants are removed.