Grand Traverse Bay is a bay of Lake Michigan formed by part of Northern Michigan. The bay is 32 miles (51 km) long, 10 miles (16 km) wide, and up to 620 feet (190 m) deep in spots. It is divided into two arms by the Old Mission Peninsula. The entire bay has a common boundary with the Grand Traverse Bay Bottomland Preserve.
Traverse City is situated at the south end of the bay where the Boardman River empties into the western arm of the bay.