The Miramichi River
watershed drains a territory comprising one-quarter of New Brunswick's territory, measuring approximately 13,000 km2 of which 300 km2 is an
estuarine environment on the inner part of
Miramichi Bay. The
watershed roughly corresponds to
Northumberland County, but also includes sections of
Victoria County,
Carleton County, and
York County and smaller parts of
Gloucester County and
Sunbury County. The Miramichi River meander length measures approximately 250 km and comprises two important branches, the
Southwest Miramichi River and the
Northwest Miramichi River, each having their respective tributaries. Nearly every bend in the river, from
Push and Be Damned Rapids to the
Turnip Patch has a distinctive name, reflecting the importance of the river to fishermen, canoeists, and lumbermen.
Tides reach upriver in the Miramichi system to
Sunny Corner on the Northwest Miramichi and to
Renous-Quarryville on the Southwest Miramichi — a distance of approximately 70 km inland from the
Gulf of St. Lawrence. The two branches combine at
Newcastle where the river becomes navigable to ocean-going vessels. The estuarine portion of the Miramichi River downriver from Newcastle in the city of
Miramichi flows through a drowned river valley.
Sea level rise in
Miramichi Bay has flooded the mouth of the Miramichi River with
saltwater. The estuary comprises the inner portion of Miramichi Bay and is protected from ocean storms in the
Gulf of St. Lawrence by
barrier islands. The estuary is significant in that it is a highly productive
ecosystem, despite its relatively small size. The estuary receives the freshwater discharge from the Miramichi River and its tributaries, mixing with organic materials from the surrounding shorelines and the saltwater inundation from the Gulf of St. Lawrence, itself an estuary and the largest on the planet. The estuary is a highly dynamic environment, ranging from the high outflows of freshwater during the spring
freshet, to the low outflow and rising saltwater content during the summer period, to fall ocean storms and
nor'easters that reshape the barrier islands and the old river channel that forms the navigation channel for ocean-going ships heading to ports at
Chatham and
Newcastle, to the winter covering of
sea ice that encases the entire estuary. The inner bay measures only 4 m deep on average, with the navigation channel measuring only 6–10 m, resulting in significant warming of estuarine waters during the summer months. The
diurnal tide cycle ranges only 1 m on average. ==Tributaries==