Great Lakes Open Water

habitat photo
Photo 1 | Photo 2 | Photo 3
Fish Island - the easternmost point in Wisconsin. Unvegetated gull island east of Rock Island. Photo by Emmet Judziewicz.

Habitat Description

Habitat Crosswalk

Cowardin: Lacustrine; littoral and limnetic (Cowardin et al. 1979).
Shaw and Fredine: Type 5: Inland open fresh water (Shaw and Fredine 1971).
Vegetation of Wisconsin: N/A (Curtis 1971).
Wisconsin Department of Natural Resources Natural Communities: Lake Michigan, Lake Superior (WDNR 2005).
Wisconsin Wetland Inventory: N/A (WDNR 1992).


Great Lakes Open Water includes the offshore and nearshore open waters of Lakes Superior and Michigan and excludes coastal marshes and tributaries (see Emergent Marsh, Inland Open Water). Offshore habitat occurs in water deeper than 80 meters and nearshore habitat ranges from 0-80 meters deep. Nearshore open waters begin at the offshore edge of the coastal wetlands where wind and wave action preclude aquatic plant growth. Nearshore habitats are warmer and more productive than offshore habitats and often support a large prey base of plankton species such as algae, cladocerans, and copepods. In the Great Lakes, fish are the dominant predator and represent the highest trophic level within open water habitats. Fish communities of Lakes Superior and Michigan contain both native species and non-native species that were either intentionally or accidentally introduced. Offshore fish communities are relatively simple and may contain lake herring, deepwater sculpin, lake trout, burbot, and deepwater cisco(extirpated from Lake Michigan). Nearshore communities can support these same species as well as lake whitefish, round whitefish, ninespine stickleback, yellow perch, walleye, and various panfish. Primary non-native species include Pacific salmon, rainbow trout, brown trout, rainbow smelt, alewife, round goby, and sea lamprey (Eshenroder et al. 1995, LMTC 2000, LSBP 2006).  

Together the five Great Lakes provide the largest single source of fresh surface water in the Western Hemisphere (GLBC 2005). Precipitation, surface runoff, and connected tributaries supply the majority of the lakes’ water and trigger annual and seasonal water level variations. Daily fluctuations or seiches also can occur from winds or changes in barometric pressure (LSBP 2006). The northernmost and largest basin in the Great Lakes is Lake Superior. With a surface area of approximately 80,300 square kilometers and a length of 563 kilometers, Lake Superior is the largest freshwater lake in the world (SWG 1993, GLRC 2005). Its surrounding bedrock has limited shoreline development and thus minimized the input of excess nutrients. Lake Michigan is the third largest Great Lake with a surface area of 58,000 square kilometers and length of 491 kilometers. It is unique among the Great Lakes because it lies entirely within United States boundaries and lacks inflow from a major river (Pautzke 1966, NRC 1992). Lake Michigan has been more adversely impacted by shoreline development than Superior because of numerous industrial and urban sites along its shores (Burgis and Morris 1987, LMTC 2000). 

Offshore islands contribute significantly to the biodiversity of Great Lakes Open Water. Although individual islands and their habitats will not be covered in detail here, their isolation from the mainland is noteworthy for many Great Lakes priority bird species. These isolated islands provide some waterbird species with secure nest sites because of fewer human disturbances and mammal predators. The Apostle Island archipelago is located entirely within Wisconsin and contains 22 islands amidst Lake Superior, 21 of which are protected by the Apostle Islands National Lakeshore (AINL) established in 1970 (Judziewicz and Koch 1993). The Grand Traverse archipelago contains 26 islands within Lake Michigan, stretching from Green Bay and Door Peninsula to the tip of Michigan’s Garden Peninsula (Judziewicz 2001).  

Historical and Present-day Context and Distribution

Retreating and advancing glaciers during the Pleistocene period formed the basins of Lakes Superior and Michigan. As the ice sheets retreated northward, meltwater accumulated in the basin between the icefront and the higher land surrounding the basin and formed pro-glacial lakes, the predecessors to Lakes Michigan and Superior (Salamun and Stearns 1978). Although their size and configuration are virtually unchanged since that time, their ecological conditions have been impaired. Significant ecological changes began in the mid-1800s when European settlement resulted in deforestation, industrial pollution, overfishing, increased sediment loads, and alteration of connected tributaries (LMTC 2000, LSBP 2006).   

Natural Disturbances and Threats

Great Lakes Open Water habitats are subject to many of the same disturbances impacting inland lakes (see Inland Open Water). Overall, they have been impaired by habitat loss, chemical contaminants, aquatic nuisance species, resource harvesting, and climate change. During the next 50 years, climate change has the potential to cause major hydrological changes and could lower lake levels by more than a meter. According to some models, air temperature, precipitation, evapotranspiration, runoff, and lake surface water temperatures will increase whereas total basin moisture, snow, soil moisture, groundwater levels, lake levels, and percent ice cover are predicted to decrease (LMTC 2000). Other models suggest more uncertainty regarding changes to annual precipitation (Mortsch and Quinn 1996, Magnuson et al. 2006). Although the biological consequences are not clear, experts predict wetland losses and continued shifts in species composition.

Native biodiversity already is much reduced in the Great Lakes because of the proliferation of non-native species such as zebra mussel, sea lamprey, and alewife. Transoceanic ships discharge their ballast water and thus inadvertently release these nuisance species to the Great Lakes (Holeck et al. 2004). Nearly one-third of non-native species introductions to the Great Lakes have occurred since the opening of the St. Lawrence Seaway in 1959. Once introduced, non-native species spread inland, frequently by way of barges, recreational watercraft, bait buckets, fish stocking, and other human-assisted transport mechanisms (LSBP 2006).

Stricter environmental regulations and increased public and industrial cleanup efforts have greatly improved water quality in recent decades but multiple stressors remain. Toxic chemicals, excess nutrients, and sediments continue to degrade the open lake system. These pollutants enter Lakes Superior and Michigan by numerous sources, such as contaminated groundwater and sediments, point source discharges, nonpoint source runoff, and atmospheric deposition. Once absorbed into lake waters, they enter a closed-system where they are trapped and continually recycled. Some of these pollutants may have immediate effects on the composition, structure and function of aquatic communities whereas others may concentrate at magnified levels higher in the food chain. Because of the importance of waterborne navigation in the Great Lakes, sediment deposition often necessitates periodic dredging. Contaminant loads in Lake Michigan are higher than Lake Superior because of greater industrial and urban development along its shore. However, many pesticides present in the Great Lakes, including DDT, likely traveled by air from as far as Mexico and Central America (Schelske and Carpenter 1992, LMTC 2000, LSBP 2006).

Offshore wind energy may provide a valuable resource for Great Lakes state, but there are several environmental issues that warrant consideration, including electromagnetic fields generated by turbines and underwater cables, noise associated with installation and operation, and fragmentation and possible degradation of habitat. In addition, wind turbines may disrupt migratory pathways or cause birds to directly collide with blades or towers (Pryor et al. 2005).

Related WBCI Habitats: Great Lakes Beach and Dune, Inland Open Water.

Overall Importance of Habitat for Birds

The open waters of Lakes Michigan and Superior provide essential foraging habitat for numerous breeding and migrating species, including several species more commonly associated with oceanic habitats. Low numbers of Pomarine and Parasitic Jaeger, Black-legged Kittiwake, and Sabine’s Gull migrate through the Great Lakes’ expansive open waters on a rare or accidental basis. During the winter, seaducks such as Surf, Black, and White-winged Scoter, Long-tailed Duck, Bufflehead, Common Goldeneye, and Common and Red-breasted Mergansers remain in ice-free waters to feed on crustaceans, mollusks, and aquatic insects (Robbins 1991, Savard et al. 1998, Roberston et al. 1999, Kessel et al. 2002, Robertson et al. 2002). Other migrant and wintering waterfowl such as Canada Goose, American Black Duck, Mallard, Canvasback, Redhead, Greater Scaup, and Lesser Scaup also forage and roost in open waters. In recent years, zebra mussels and quagga mussels have proliferated in the Great Lakes and become an important food item to several diving duck species, especially scaup. Unfortunately, zebra mussels bioaccumulate toxins and thus can adversely affect the reproductive success of species consuming them (Custer and Custer 1996, Mazak et al. 1997, Austin et al. 1999).

Nearshore and offshore fish communities provide abundant prey for piscivorous bird species. Less than 200 meters from shore, Common and Caspian Terns dive for alewife, rainbow smelt, yellow perch, trout-perch, and lake shiners (Cuthbert and Wires 1999, Nisbet 2002). Bald Eagles and Ospreys generally forage less than 500 meters from shore and capture various panfish, suckers, and other shallow water or surface-dwelling fish species (Gieck 1986a, Gieck 1986b, Buehler 2000, Poole et al. 2002). Common Loons often forage in open waters surrounding shoals, islands, and rock outcrops (McIntyre and Barr 1997, Mallory and Metz 1999, Titman 1999, Kenow et al. 2002). Post-breeding Red-necked Grebes stopover in the Great Lakes not only for their abundant fish prey, but also because the lakes’ size and relative inaccessibility provides safe molting areas (Stout and Cooke 2003). Horned Grebe, Bonaparte’s Gull, Herring Gull, Ring-billed Gull, and Double-crested Cormorant are other important piscivorous species of Lakes Superior and Michigan. In the last two decades, dramatic population increases of Double-crested Cormorant, Ring-billed Gull, and Herring Gull in the Great Lakes region have resulted in human conflicts on several safety, health, economic, and environmental issues (Gabrey 1996, Stapanian and Waite 2003). The Double-crested Cormorant is perhaps the most persecuted because of its perceived competition with recreational and commercial fishing interests, yet few data exist to corroborate a significant economic impact (Kuslan et al. 2002). To the contrary, stomach content analyses from cormorants on Lakes Superior, Michigan, and Huron found forage fish such as alewife and sticklebacks to be more prevalent than commercially important fish. Another Lake Superior study found no evidence that cormorants consumed either lake trout or common whitefish, which are the two most important commercial fish there (Craven and Lev 1987, Ludwig et al. 1989 cited in Hatch and Weseloh 1999).
Several species that forage in Great Lakes Open Water also nest on offshore islands. Double-crested Cormorant, Ring-billed Gull, Herring Gull, Caspian Tern, and Common Tern nest colonially in the Apostle Islands and Grand Traverse archipelagos (Judziewicz and Koch 1993, Matteson et al. 1999, Judziewicz 2001, Hebert et al. 2005). Isolated islands are important to colonial-nesting waterbirds because of their proximity to feeding territories and protection from predators and human disturbances. The competition for secure colony sites is great and can result in exclusion of certain species. The decline of Common and Caspian Terns in Wisconsin is attributed in part to interspecific competition with Ring-billed and Herring Gulls on these islands (Matteson 1988). Large colonies also may change the character of the island by causing tree loss or vegetative succession and thus lessen its suitability as a colony site. In order to sustain regional populations, it is essential to protect existing colonies and maintain alternate colony sites, such as dredged material islands (Kushlan et al. 2002).

Priority Birds

Species Status Habitat and/or Special Habitat Features
Trumpeter Swan m  
Tundra Swan m  
Canada Goose
(Mississippi Valley Population)
American Black Duck m  
Mallard m  
Canvasback m, w  
Redhead m, w  
Lesser Scaup F, M Migrant in open waters with abundant amphipod populations.
Horned Grebe M  
Red-necked Grebe f, m  
Osprey f, m Forages in nearshore areas with high abundance of fish.
Bald Eagle f, m Forages in nearshore areas with high abundance of fish.
Caspian Tern F, M Nests on sparsely vegetated offshore islands.
Common Tern F, M Nests on sparsely vegetated offshore dredge spoil islands and former pier remnants.


Stay tuned……. will incorporate habitat acreage objectives from Upper Mississippi River and Great Lakes Region Joint Venture Implementation Plan.

Management Recommendations

Landscape-level Recommendations

  1. Prevent the introduction of additional exotic species and slow the spread of existing aquatic invasives through improved regulation, management, and education. Coordination and cooperation across jurisdictional boundaries is critically important.
  2. Limit factors potentially reducing water levels and outflows to maintain open water habitat and protect against predicted impacts of climate change.
  3. Reduce loadings and emissions of critical pollutants at Lakes Michigan and Superior to improve water quality and habitat conditions.
  4. Incorporate waterbird conservation actions into fisheries management policies and programs. 
  5. Limit the lethal control of abundant waterbirds only to circumstances where economic impacts are clearly proven and sustainability of the regional population is not jeopardized (Kushlan et al. 2002).
  6. Develop outreach programs that help bring public perception of locally abundant waterbirds in line with scientific and economic findings (Kushlan et al. 2002).

Site-level Recommendations

  1. For new or enhanced nest colonies, managers should: 1) assist in designing dredge-spoil or other islands to ensure sites are suitable for a colony; 2) provide sparsely vegetated substrate on potential nest islands for terns; 3) deter and control Ring-billed and Herring Gulls where they may displace terns (Matteson 1988); 4) deter and control mammalian predators (mink, raccoon, etc.); and 5) consider feeding territories of existing tern colonies when locating new projects (Souilliere et al. 2007).
  2. All accessible colonies and roost sites should be identified to the public, posted and protected, and anti-disturbance policies developed and implemented as needed (Kushlan et al. 2002).

Ecological Opportunities

Ecological Landscape Opportunity Management Recommendations
Central Lake Michigan Coastal Major All
Northern Lake Michigan Coastal Major All
Superior Coastal Plain Major All
Southern Lake Michigan Coastal Major All

Research Needs

  1. Develop and implement standardized, systematic waterbird surveys in Great Lakes open waters to determine distribution, abundance, trends, habitat use, and migration chronology (Stapanian and Waite 2003, Souillere et al. 2006).
  2. Implement a Great Lakes winter survey to measure abundance and trends of sea ducks (SDJV 2002).
  3. Identify suitable offshore wind development locations that are away from migratory pathways and important nesting and feeding areas (Pryor et al. 2005).
  4. Implement conservation strategies as described in the Great Lakes Waterbird Conservation Plan (in press).
  5. Improve bioenergetics knowledge of piscivorous birds and their prey in Great Lakes open waters.
  6. Develop non-lethal methods to reduce real and apparent impacts of waterbirds in urban and suburban landscapes (Kushlan et al. 2002).
  7. Determine the effects of contaminants on waterbirds, especially implications at the population level, contamination sources, pathways to birds, sublethal effects, and synergistic effects. Long-term monitoring programs and tissue repositories are needed for this effort (Kushlan et al. 2002).


Key Sites

Key Partners

Funding Sources

Information Sources


Contact Information

Kreitinger, K., Y. Steele and A. Paulios, editors. 2013.
The Wisconsin All-bird Conservation Plan, Version 2.0. Wisconsin Bird Conservation Initiative.
Wisconsin Department of Natural Resources. Madison, WI.

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