Oregon Sea Grant

The Laurentian Great Lakes are the crown jewels of the freshwater systems of North America. These five large lakes, their associated lakes, and their connecting channels (fig. 1) hold about 23,000 km³ of water—enough to cover the contiguous United States to a depth of about 3 meters (Great Lakes Environmental Atlas 1995). They comprise a series of ecosystems unique in the world and are the subject of considerable study, regulation, and observation. They also possess physical, chemical, and biological characteristics unique among all the largest lakes on the planet. Yet for all their immense size and grandeur, the Great Lakes have not been protected from anthropogenic perturbations, which have changed them on a basin-wide scale.

The fishes of the Great Lakes, like all the aquatic flora and fauna, are completely dependent on their surroundings for their long-term survival. The primary objective of this chapter is to provide a broad-brush review of the key non-biological aspects of the Great Lakes that, in turn, provide the essential habitat for the fishes. Without the unique geology, physics, and chemistry of the lakes, as described in this chapter, the likewise unique fishes of the lakes could not survive or continue to evolve.

This chapter includes three sections: Lake Formation and Geology, Overview of the Great Lakes’ Physical Characteristics, and Great Lakes Water Chemistry. These sections discuss a wide variety of topics but place  emphasis on changes to the Great Lakes over the past forty years. Examples used in this chapter come from all five Great Lakes but do not cover every aspect of the geology, physics, or chemistry for each lake. Representative information is presented to demonstrate general trends of the Great Lakes with the understanding that each Great Lake has followed a different course in the past two hundred years. Each section is intended to provide background information that, in turn, sets the stage for the richer discussion of Great Lakes fishes found in the succeeding chapters.

Despite their immense size, the Great Lakes have been irreversibly changed. Human induced impacts have touched virtually every aspect of the Great Lakes, including its habitats, landscape, and water chemistry. The chapters that follow illustrate how demographics, landscape changes, climate change, non-native species introductions and invasions, contaminants, fish diseases, massive fishing pressure, and regulatory missteps have led to the demise of the Great Lakes, in general, and many fish species, in particular. The crises induced by anthropogenic activities in the mid-twentieth century forced the hands of the two nations that border the Great Lakes, the United States and Canada, to create a more sustainable approach to managing these huge ecosystems.

Today, we greatly benefit from a thoughtful and carefully crafted ecosystem-based management (EBM) approach in the Great Lakes region. The formation of EBM is proving as important to the survival of Great Lakes fishes as the non-biological aspects of the lakes. Just as the physics and water chemistry of the Great Lakes have changed for the better in the last half-century, so too has our management evolved.