Aythya marila, commonly known as the Greater Scaup, is native to regions across the northern hemisphere. Its geographical distribution includes parts of North America, Europe, and Asia. In North America, it is predominantly found in the boreal forest and tundra zones of Alaska and Canada during the breeding season. In Europe and Asia, it breeds in the northern parts, such as Iceland, Scandinavia, and the Russian taiga.

The Greater Scaup typically inhabits freshwater lakes, large ponds, and coastal waters during the breeding season. These environments are characterized by cool, temperate to subarctic climates. During the winter, it tends to migrate to coastal marine environments, estuaries, and larger inland lakes that remain unfrozen.

Aythya marila occupies an ecological niche as a diving duck, feeding primarily on aquatic invertebrates, mollusks, and plant matter. Its presence in both freshwater and saline environments showcases its adaptability. The Greater Scaup's foraging behavior and dietary preferences contribute to the control of invertebrate populations in these aquatic ecosystems. Its migratory habits also facilitate nutrient flux between different geographic regions.