Q.Saginaw Bay - Size and Depth A. Total surface area is approximately 1,143 square miles. The inner bay (from Sand Point and Point Lookout to the mouth of Saginaw River) has an average depth of 15 feet and a maximum depth of 46 feet.
The outer bay (from Sand Point and Point Lookout to Au Sable Point AND Port Austin) has an average depth of 48 feet and a maximum depth of 133 feet.
