Shallow, circular or slightly elongated basins with simple shorelines and wide entrances that are open to the ocean.
These estuaries are generally subtidal, with small intertidal areas which are restricted to the sheltered headwaters of the more elongated types.
There is little input from the river and circulation in the estuary is weak.
The estuary entrances are wide and open to the ocean, allowing swell to enter the bay and resuspend seabed sediments, meaning that the movement of the water in the estuary is dominated by the ocean.
There are no sand bars or shoals on the ocean side of the entrance. Two-dimensional mixing due to wind and sedimentation due to waves do occur, and as a result the estuary bottom sediment is sandy, except in shallower areas where there is less wave-driven resuspension.
Category D estuaries are representative of features commonly called coastal embayments.