The estuary is a highly dynamic environment, subject to high freshwater outflows during the spring freshet, low outflow and rising saltwater content during the summer period, fall ocean storms and nor'easters which reshape the barrier islands and the old river channel, and winter sea ice which encases the entire estuary.

Continued sea level rise is very slowly inundating adjacent low-lying areas and promoting rapid erosion of the low sandstone cliffs bordering the bay.

The estuary receives the freshwater discharge from the Miramichi River and its tributaries, giving local waters somewhat lower salinity.

Organic materials from the surrounding shorelines and inflowing rivers contribute, together with the warm water, to the bay's high productivity.

[4] Recreational uses in Miramichi Bay include windsurfing, boating, kayaking[2] as well as fresh and salt water fishing.

Birdwatching is also common near Miramichi Bay because of the scenic views and habitat friendly area for many varieties of migrating birds.