The inlet is a wave dominated estuary with a high sediment trapping efficiency, it is always open to the ocean and the water is turbid.

The total surface area of the inlet is 20 square kilometres (8 sq mi).

[1] Hardy Inlet is the wide, lower basin of the Blackwood Estuary with a long narrow and shifting[2] entrance channel.

[3] Algal blooms have been recorded in the inlet around Molloy Island and West Bay as a result of elevated nutrient levels, particularly Nitrogen and Phosphorus levels.

Warnings have been issued so that people do not consume shellfish such as mussels and oysters which can filter out the toxic algae.