The underwater features of the seabed sculpted during the lower sea levels of the ice ages make the gulf a semi-enclosed sea bounded to the south and east by underwater banks. Georges Bank in particular, on its southern end, shelters the gulf from the Gulf Stream. Gulf of Maine waters are more strongly influenced by the Labrador Current, making the gulf waters significantly colder and more nutrient-rich than those found to the south. Undersea valleys in the central basin can reach depths of , while undersea mountains rise up from the sea floor, almost reaching the surface in some locations, or even exceeding it, creating islands.