Dune and swale complexes are series of roughly parallel dunes that form as the water level of the lake gradually drops. These dunes may form in bays which are gradually being filled in by sand deposits. Wilderness State Park on the north shore of Lake Michigan has more than 100 dunes in a dune and swale complex.

The complex is produced by a series of foredunes forming as the beach "grows" out into the lake. (See Foredunes for foredune descriptions and formation.) Each new foredune eventually cuts off the sand supply to the inland dune. The result is a series of low dunes, generally less than 3 meters (15 feet) in height.

Swales are the troughs or low-lying land separating the dune ridges. Originally wet and marshy, the swales dry out over time. The progression from wet to dry swales can be seen as one moves further inland.

Dune vegetation in the complex also reflects the age progression of the dunes. Pioneering species grow on the active foredune. Inland dunes have progressively older and more established ecosystems on them.