Delta Marsh has existed for at least 2,500 years. It was formed when a peninsula was eroded by counter-clockwise currents in Lake Manitoba, causing deposition of a "barrier beach" along the southern lake shore. A portion of the lake was thereby isolated, creating the marsh.
The following series of diagrams illustrate the sequence of events leading to the creation of Delta Marsh following the retreat of the Laurentide glacier about the 10,000 years ago, and the conversion of glacial Lake Agassiz into the modern Lake Manitoba.
Thanks to Dr. Jim Teller (Dept. of Geological Sciences, University of Manitoba) for permission to use these modified diagrams, originally published in his paper: J.T. Teller & W.M. Last 1981. Late Quaternary history of Lake Manitoba, Canada. Quaternary Research 16:97-116.