A Late Summer’s Day in the Marsh

There is no place like a marsh in the dog days of summer. Dense patches of cattails sway like waves in the breeze, a breeze carries the trilling of a red-winged blackbird and the aroma of blossoming milkweed. In the golden light, a jewel-toned dragonfly speeds through the air with the agility of a fighter pilot. 

Marshes, swamps, bogs, fens: no matter what you call them, wetlands – places where the ground is saturated with water for most or all of the year – are critically important for a variety of plant and animal species, including many that are threatened or endangered. Coastal wetlands in particular serve as important nursery and foraging habitats for many fish species, but they are also among the most vulnerable ecosystems globally to human-caused changes1.

When you hear the phrase “coastal wetland,” you might think of mangroves or salt marshes at the edge of the ocean, but there are also freshwater coastal wetlands! For example, wetlands that are directly connected to the waters of the North American Great Lakes are also considered “coastal”, and like their marine counterparts, they provide a ton of benefits for humans (also called ecosystem services). Coastal wetlands protect shorelines from erosion, prevent flooding by retaining excess water during storms and releasing it slowly over time – basically like giant sponges – and act as the planet’s kidneys, filtering runoff from the surrounding land and improving downstream water quality.  

Whether salty or fresh, coastal wetlands punch way above their weight when it comes to the benefits they provide. (Left: Mangrove forest, credit: Pixabay, Right: Cattail marsh, credit: K. O’Reilly)

Like coral reefs and rainforests, Great Lakes coastal wetlands teem with life, including many fish species that are recreationally important. Many Great Lakes fish species depend on coastal wetlands at some point during their life cycles, with species such as Northern Pike (Esox lucius), Yellow Perch (Perca flavescens), and Largemouth Bass (Micropterus salmoides) relying on these habitats when they are young2.

Baby bass, doo, doo, doo, doo, doo, doo (credit: K. O’Reilly)

Although they make up a small fraction of the lakes’ surface areas, Great Lakes coastal wetlands often face the highest number of stressors because they represent the primary interface with humans3. Over half of historic coastal wetland area has been lost since European settlement of the Great Lakes basin4, and while the rate of loss has slowed due to state and national protection measures, new threats such as non-native species and climate change threaten remaining wetlands. Not to mention, many of the most pressing environmental challenges facing the Great Lakes – water quality concerns, decreasing fisheries, and increased flooding – are tied to the historic decline in coastal wetland area. To combat these challenges and maintain the benefits wetlands provide, it’s critical to make sure remaining habitats are in good shape.

Many coastal wetlands – especially in the southern part of the Great Lakes basin – face a variety of threats. At this wetland in downtown Monroe, Michigan, for example, the plant community was dominated by the invasive Phragmites australis (common reed) and the water quality was impacted by run-off from the surrounding urban landscape. (Credit: K. O’Reilly)

Enter: the Great Lakes Coastal Wetland Monitoring Program (CWMP), a binational collaboration of U.S. and Canadian groups including federal agencies, states, and universities working together in a standardized way to monitor the health of coastal wetlands throughout the Great Lakes basin5. With funding from the Great Lakes Restoration Initiative, this group has sampled over 1,000 coastal wetlands since the program began in 2011. When CWMP crews visit a wetland, they give the whole ecosystem a “check-up” by taking measurements of water quality parameters including dissolved nutrient concentrations (like nitrogen and phosphorus) as well as doing surveys of invertebrate, fish, amphibian, and bird communities.

Field crews from the University of Notre Dame sample a Great Lakes coastal wetland fish community using fyke nets. (Credit: K. O’Reilly)

CWMP provides baseline information about the health of coastal wetland ecosystems that can indicate human impacts over time such as changes to water quality resulting from human land use6. Additionally, CWMP surveys have revealed new locations of non-native species such as the New Zealand mud snail (Potamopyrgus antipodarum). The collected data help managers make informed decisions about how to prioritize protection and restoration efforts. A manager can use the program’s online mapping tool to select a specific wetland and see reports from every sampling event.

A screenshot of the Great Lakes coastal wetland mapping tool available at http://www.greatlakeswetlands.org.

By monitoring coastal wetlands, scientists are not only working to keep a finger on the pulse of these unique and globally important ecosystems, but also to ensure that future generations can enjoy a summer’s day in the marsh.

Kayaking in a Lake Michigan coastal wetland (Credit: K. O’Reilly)


  1. Zedler, J.B., & Kercher, S. (2005). Wetland resources: status, trends, ecosystem services, and restorability. Annu. Rev. Environ. Resour., 30, 39-74. https://doi.org/10.1146/annurev.energy.30.050504.144248  
  2. Jude, D.J., & Pappas, J. (1992). Fish utilization of Great Lakes coastal wetlands. Journal of Great Lakes Research, 18(4), 651-672. https://doi.org/10.1016/S0380-1330(92)71328-8 
  3. Allan, J.D., et al. (2013). Joint analysis of stressors and ecosystem services to enhance restoration effectiveness. Proceedings of the National Academy of Sciences, 110(1):372–377. https://doi.org/10.1073/pnas.1213841110 
  4. Brazner, J., et al. (2000). Assessing the ecological importance of coastal wetlands in a large lake context. Internationale Vereinigung für theoretische und angewandte Limnologie: Verhandlungen, 27. 1950-1961. https://doi.org/10.1080/03680770.1998.11901583
  5. Uzarski D.G., et al. (2017). Standardized measures of coastal wetland condition: implementation at a Laurentian Great Lakes basin-wide scale. Wetlands, 37:15–32. https://doi.org/10.1007/s13157-016-0835-7
  6. Harrison, A.M., et al. (2020). A basin-wide survey of coastal wetlands of the Laurentian Great Lakes: development and comparison of water quality indices. Wetlands, 40(3), 465-477. https://doi.org/10.1007/s13157-019-01198-z

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