Pritchard (1952) has suggested a topographic classification of three groups:

Coastal plain estuaries: Coastal plain estuaries, or drowned river valleys, were formed as the melting waters from the last ice age flooded the existing river valleys. River flow is normally small compared to tidal prism (the volume of water between high and low tides) and sedimentation has not kept pace with inundation. The resulting estuary has maintained the topography of the former river valley but is relatively shallow (rarely deeper than 100 feet (30 metres)). There are extensive mud flats with a sinuous, deeper central channel. Coastal plain estuaries are generally found in temperate latitudes. Examples are the Chesapeake Bay estuary system in the United States and the Thames and Mersey systems in England.

Fjords: Fjords, estuaries that have been formed by glacial erosion, generally occur at higher latitudes, are relatively long and deep, and possess a shallow sill at the fjord mouth and fjord intersections. These shallow sills can restrict the free exchange of ocean and estuary waters, in some cases producing a small tidal prism with respect to river flow. Examples of fjords are Puget Sound (United States), Alberni Inlet (British Columbia, Canada), Sogne Fjord (Norway), and Milford Sound (New Zealand).

Bar-built structures: Bar-built estuaries are formed by the same processes as the drowned river valleys. The difference is that sedimentation has kept pace with inundation, with a characteristic bar forming at the mouth. Associated with depositional areas, bar-built estuaries are shallow with extensive lagoons and waterways inside the mouth. Entrance velocities can be quite high but quickly diminish as the estuary widens. This type of high sediment volume estuary is most often found in tropical or active coastal deposition areas. Examples of bar-built estuaries are the Roanoke River (United States) and the Vellar Estuary (India).

Other: A fourth group of estuaries would be those not belonging to the previously mentioned three. This group would include estuaries formed by volcanic eruptions, faulting, landslides, or other processes.