n. — Geography
a shallow bay that abuts a lake or a stretch of a river.
Type: 3. Semantic Change — The term back bay is used to describe a shallow and quiet body of water (see the 2006 quotation) attached to a lake (see the 2014 quotation); accordingly, back bays are often discussed in contrast to "the main lake" (see the 1991 and 2005 quotations). A back bay is often a prime fishing location (see the 1988, 2000 and 2013 quotations). The term back bay does not appear in our non-Canadian dictionaries (e.g. DARE, OED).
See also COD-2, s.v. "back bay", which is marked "Cdn".