Swamp Vs Marsh – What’s the Difference? (Explained)

With many dozens of types of wetlands defined within half a dozen categories and classes (and even those depend on which classification system is used!), it’s no wonder different wetland types are often confused for one another, with small ponds often being called bogs, marshes being called swamps, and so on. However, there are clear differences between each different wetland type; none are synonymous.

While marshes and swamps are indeed more alike than not, here we’ll delve into exploring their similarities and differences, as these two wetlands are often mistaken for one another, their titles incorrectly used interchangeably. For our concise and informative guide to wetland classification, click here.

Similarities Between Swamps and Marshes

1) Structure and Formation

According to the Cowardin System of wetland classification, there are five classes of wetlands that can be broken down into many types and subtypes. These classes are: marine, riverine, estuarine, lacustrine, and palustrine. Both swamps and marshes belong to the latter-most group of palustrine wetlands, which are those that are dominated by trees, shrubs, and emergent vegetation. They are also often home to many species of mosses and lichens, though this isn’t exclusive to the palustrine class. Palustrine wetlands are the ones that many of us are the most familiar with, as this class also includes bogs and fens.

Additionally, both swamps and marshes can be either inland or coastal and contain either fresh or saltwater but should have a salinity of .5 parts per thousand (ppt) or lower. Both swamps and marshes are constantly saturated, but these water levels can fluctuate in accordance with the season, precipitation, and the water level of any water bodies feeding the swamp or marsh, such as a lake, river, or the ocean.

Marshes and swamps are typically formed when a significant water body, such as a large lake, river, or ocean, floods either seasonally or permanently. This alters the composition of the area to such a degree that new plant and animal life are able to take hold, resulting in a marsh or swamp depending on the location and plant life.

2) Functions and Benefits

Both swamps and marshes are, like all wetlands, among the most valuable and productive ecosystems on Earth, serving a vast array of benefits to both the natural world and humans.

Perhaps the most notable of these benefits is their ability to control flooding, protecting surrounding ecosystems and human areas from potential damage by soaking up and holding onto excess water. They also provide valuable nutrient removal via their plants, which are quite adept at utilizing excess nutrients and even pollutants that come their way. This helps prevent things like agricultural runoff, fertilizers, and sediment runoff from high precipitation from getting deposited into water sources and environments that could then harm wildlife and humans alike. The ability of these wetlands to cycle nutrients and water is virtually unparalleled, and also helps to prevent algal blooms in any connected coastal or inland waters.

In fact, the Everglades, a 2,000 square mile marsh, in Florida are responsible for helping to provide clean drinking water as well as protection from coastal storms. However, this giant marsh used to be more than double that size, but human development continues to shrink it. This has resulted in Florida experiencing significantly more flooding, reduced access to clean drinking water, and a severe loss of unique plant and animal life.

Similarly, the historically immense wooded bayous and swamps of New Orleans have shrunk by approximately 50% due to being filled in, dammed, and developed. This has resulted in massive (and massively expensive) issues with flooding and wind damage, particularly during hurricane season, and a noticeably rapid rate of sinking below sea level. In fact, a study conducted by NASA noted, “the primary contributors were found to be groundwater pumping and dewatering (surface water pumping to lower the water table, which prevents standing water and soggy ground)” – that is to say, the filling in of swamps.

3. Species That Call Them Home

Marshes and swamps are both home to a broad variety of waterfowl, reptiles, amphibians, songbirds, fish, and mammals. Shared species between the two (depending on the exact location as well as the type of swamp or marsh) can include alligators, great blue herons, egrets, a variety of warblers, muskrats, rabbits, and river otters.

Differences Between Swamps and Marshes

You’ll notice some of the same categories here as in the “Similarities” section above, as marshes and swamps hold things in common as well as in contrast within these categories.

1) Structure and Formation

Though marshes and swamps have some similarities in their structure, there are also many differences. Perhaps the most obvious of these include their vegetation. Swamps are characterized by being dominated by trees and some shrubs, with many swamps existing in forests. Examples of swamps include cypress swamps, mangrove swamps, and northern hardwood swamps – all of these are so named for the trees that characteristically inhabit them.

The incredibly nutrient-rich soils of swamps enable them to have a great diversity in plant and animal life. These soils can be alkaline, neutral, or acidic, further adding to the potential diversity of these incredibly unique wetlands. Swamps often have lower water levels during prime growing seasons (the warmest time of the year), sometimes consisting of just muddy, saturated soils, but can also be fully submerged in many feet of water at any time.

Marshes, by contrast, have soils that are more mineral-rich, consisting of some combination of either sand, silt, clay, or all three, resulting in a pH that is most often neutral but can be on the slightly more alkaline end. Though certainly not nutrient-poor by any means, marsh soils contain fewer nutrients overall than those of most swamps. They are characterized by the presence of emergent shrubs and herbs rather than trees.; though marshes can certainly have trees, they won’t be dominated by them like a swamp. They will generally always have at least some standing water, ranging from an inch or two to several meters. The exception to this is a type of marsh known as a prairie pothole, which can dry out completely for portions of the year.

Typically, marshes form along shallow lakes, rivers, or ocean edges. The same is true of swamps, but, again, the difference lies in plant type and composition. Generally, a waterbody that floods in the woods can form a swamp, and one that floods in more open land can form a marsh.

2) Species That Call Them Home

Although swamps and marshes house many similar species, they are also home to very different life, as well. Most notably, it is the plant life that differs. As previously noted, swamps are dominated by trees that are tolerant of (and even thrive in) flooded conditions, such as cypress, willows, cottonwoods, mangroves, and many others. Their forested nature means they can also host mammals such as beavers, deer, foxes, and raccoons. While these can all certainly be found in marshes, they are more common in swamps. In southern swamps, tree-loving panthers (subspecies of mountain lions) and bobcats can also be found.

Marshes, on the other hand, are dominated by emergent vegetation, namely sedges and reeds, but can also include bulrushes, lily pads, pickerelweed, and many others. Many similar animal species can be found, excluding those (like beavers and panthers) that rely more heavily on the presence of trees.

3) Human History and Perception of Swamps and Marshes

Unfortunately, swamps have historically been viewed quite negatively by people, particularly in the US and Europe. Their rich soils, constant saturation, a forested nature resulted in them being perceived as dark, malevolent, stinky, and infested with insects like mosquitos. Folklore and pop culture have both fed these ideas, painting a picture of swamps as the grim and evil home to snakes, alligators, biting insects, sticky and deep mud, and dark spirits. These misconceptions and their continued pervasiveness fueled by pop culture villains like Swamp Thing are large contributors to why we have destroyed, drained, and filled in many swamps around the world. This has been a particular issue in the U.S..

Although marshes have also had more than their fair share of getting drained and filled in to create land for farms and towns, they overall have a somewhat more favorable perception than that of swamps. Coastal marshes serve as incredibly important nurseries for young fish that are highly sought-after by fishermen, such as pollock, Atlantic herring, and some flounder species. The combination of providing a source of food as well as economic value has somewhat boosted marshes in the eyes of people. Additionally, their overall lack of trees creates an open space that is bright and visually appealing to look at, allowing one to see the plethora of waterfowl with little encumbrance. The low-growing vegetation and open nature of marshes also enable relatively easy access by boat and kayak, whereas swamps can be somewhat difficult to navigate.

A Final Note of Hope 

Thankfully, the metaphorical tides are turning. We now understand that swamps, like other wetlands, are among the most valuable ecosystems in the world. Their rich soils give rise to a vast array of life, protect us from flooding, and provide indigenous and modern peoples alike with ample food like fish, shrimp, clams, and nutrient-dense plants like swamp cabbage and water chestnut. Even the insects are an invaluable boon, providing food for a vast array of animals, and many of them also serve as pollinators. Wetlands, including swamps and marshes, act as critical carbon sinks, responsible for capturing and storing over one-third of the world’s carbon.

We would like to end with the note that many wetlands, particularly swamps but including marshes, are still often viewed as “wastelands” or “unproductive” and thus destroyed to ironically create land that is, by comparison to wetlands, a monoculture of unproductivity. Our hope is that these wetland articles can serve as gentle eye-openers and educate others on their incredible value and importance, uniqueness, and beauty.