There are multiple theories about the origin of the name "Casco Bay". Aucocisco , an Anglicisation of the Abenaki name for the bay, means "place of herons", "marshy place", or "place of slimy mud". York said there are "little more than two hundred". Casco Bay spans about square miles, with its shore stretching miles.
Researchers with the U. Geological Survey have dated volcanic material embedded in exposed bedrock in Casco Bay to the Ordovician period roughly million years ago, [ 8 ] predating the formation of the Atlantic Ocean by some million years. Around 14, BCE during the Wisconsin glaciation period at the end of the last glacial cycle , the Laurentide ice sheet covering the Casco Bay region began to recede, according to radiocarbon dating on marine shells and other materials.
A Phippsburg hill called Fuller Mountain has the bay's highest elevation along the immediate shoreline, estimated at feet above sea level by the U. Geological Survey in , and feet on more recent topographical maps. In Casco Bay's western reaches, a line of islands extends west from Chebeague to Cushing Island to create protected anchorages for vessels, as do the narrow peninsulas that jut into the bay's eastern section.
Casco Bay's topography produces a tidal range of about nine feet on average. Seawater circulates counterclockwise into Casco Bay via the Gulf of Maine Gyre, which is formed from cold water that passes over the Scotian Shelf off Nova Scotia , then in and out of the Bay of Fundy. The Presumpscot River is the largest single source of non-saline water emptying directly into Casco Bay, [ 21 ] flowing south from its headwaters at Sebago Lake , Maine's second-largest lake.
Water temperatures in Casco Bay rose by 3 degrees Fahrenheit over a three-decade period through , with some scientists linking the change to shifting mixes of organisms and wildlife in the bay. In a study of invasive species threatening Casco Bay eelgrass and kelp beds that other organisms and wildlife depend on, researchers found abundant evidence of the presence of several types of tunicates , bryozoa , Japanese skeleton shrimp and at one location European green crabs. Casco Bay has an estimated 16, acres of intertidal habitats to include mudflats , marshes, beaches and rock formations according to the National Wetlands Inventory, [ 27 ] supporting a range of biota and wildlife.
