Hannah Bay is located in the extreme southern end of James Bay, just west of the Ontario-Quebec border. The largest river, the Harricanaw, empties into the bay from the south, as does the Kesagami, which joins the Harricana at its mouth. A third major river, the Missisicabi, empties into the extreme northeastern corner of the site. The silt deposited by these rivers has created extensive shoals that extend as far as seven to eight km from the high tide line. At low tide, the bay becomes a tidal flat that is as much as 15 km wide. These tidal flats are largely composed of hard-packed silts and clays, and the water in the bay is turbid and brackish. Hannah Bay has among the widest expanses of marshes (approximately 1.5 km in width) along the James Bay coast. The shoreline of the bay is characterized by meadows of rush and sedge, with small ponds and marshy areas being located between the elevated beach ridges along the shoreline.
The extensive mud flats and marshes of Hannah Bay support tremendous concentrations of migrating geese. At least half of the Atlantic Brant (ssp. hrota) population (maybe more) congregate here during both the spring and fall migration. In the late 1970s as many as 100,000 Brant were observed at this site during the fall migration. Although specific numbers appear to be lacking, spring staging is expected to be about the same as during the autumn. The number of Brant expected to be using the bay is about the same today as it was in the 1970s. Even larger numbers of staging Snow Geese have been recorded at this site. In the 1970s, as many as 300,000 were observed, which represented about one-fifth of the Lesser Snow Goose population at that time. Apparently, there has subsequently been some decrease in the population of Snow Geese using the bay, but the number using the area today is still of global significance.
Large concentrations of ducks and shorebirds have also been recorded at Hannah Bay. However, no recent surveys have been completed. In the 1940s, one-day counts included 4,000 Northern Pintails, 900 American Black Ducks, 400 Green-winged Teal, and 1,500 Dunlin. It is likely that these species still occur in significant numbers at this site.
Although the site is not significant as a breeding area, there is some usage of offshore islands by colonial water birds. In 1993, three nesting species were present: Ring-billed Gulls (250 nests), Herring Gulls (25 nests), and Common Terns (15 nests).
BirdLife International (2022) Important Bird Areas factsheet: Hannah Bay. Downloaded from http://www.birdlife.org on 20/01/2022.