The Detroit River is the section of the Great Lakes/St. Lawrence watershed joining Lake St. Clair from the north to Lake Erie on the south. The IBA extends from the north end of Fighting Island to the mouth of the river.

Fighting Island, with its gull and former tern colonies, lies in Canadian waters immediately downriver from Windsor. At the mouth, the river is about 6 km wide, and has several islands that range in size from over 20 km² (Grosse Isle), to less than 1 km² (numerous small islands created by dredging spoils from the shipping channel). The Detroit River freezes only occasionally; the strong current and thermal discharge from both Detroit and Windsor keep the river, or portions of it, open. In some winters, when Lake St. Clair and most of the St. Clair and Detroit Rivers freeze, exceptionally larger numbers of waterfowl will concentrate in the remaining areas of open water.

At least four species of birds are regularly present in significant numbers along the lower Detroit River: Ring-billed Gulls during the breeding season, and three species of waterfowl (Canvasbacks, Redheads, and Common Mergansers) during the late fall and winter.

In 1990, the number of nesting Ring-billed Gulls on the north end of Fighting Island was 34,021 pairs. This may represent as much as 3.9% of the estimated North American breeding population, and as much as 5.6% of the estimated Canadian breeding population. The colony has grown quickly; no Ring-billed Gulls were recorded at this site in the late 1970s. Small numbers of Common Terns nest here (33 nests in 1995), although some years they are entirely absent.

For several decades, the Lower Detroit River has been identified as a significant late fall staging and wintering area. On average, more than 8,000 Canvasback (greater than 1% of the estimated North American population), and 7,000 Common Mergansers (greater than 1% of the estimated North American population) are recorded each year during the annual Christmas Bird Count centred on Rockwood, Michigan. Redheads are also occasionally recorded along the entire river in numbers that exceed the global threshold, with nationally and possibly continentally significant numbers occurring more regularly in specific sections (such as Crystal Bay on the Canadian side of the river). Other waterfowl species commonly observed on the river include: Greater Scaup, Lesser Scaup, Common Goldeneye, and Bufflehead.

The cities of Windsor (Canadian side) and Detroit (American side), along with their associated suburbs and other smaller urban centres, lie on both sides of the Detroit River. The river itself is a busy shipping lane, with traffic occurring throughout most of the year and only a short stoppage during the winter months. Consequently, the river is subject to much pollution from the urban and industrial areas as well as risk of oil and other spills from the shipping traffic. The important wetland / wildlife values of the lower Detroit River are identified in the Detroit River Remedial Action Plan documents, and the Great Lakes Cleanup funds have been targeted for this area. In addition, the marshes at the mouth of the Canard River (which empties into the Detroit River) are identified in Ontario Eastern Habitat Joint Venture Implementation Plan as a Class II Priority Securement Site, to protect the value of the area to staging waterfowl. Disturbance at the Fighting Island Gull colony is restricted mostly to off-shore boat traffic; access to the island is controlled strictly by the owners.