Marshes are really just flooded wetlands. Most of the plants growing in the marsh are in shallow water. These kinds of plants are called emergent plants. Some examples of marshes are the Florida Everglades, the prairie potholes of central North America, numerous coastal areas along the Great Lakes, and salt marshes along middle and high-lattitude ocean coasts all over the world. The way they perform this function is that they hold floodwaters and release water, slowly reducing flood damage.
Swamps are mostly trees or shrubs that are in a variety of flooding conditions.
It's usually standing water all year around. Swamps vary a lot when it comes to how many nutrients and minerals are in its soil. Some examples of swamps are the hardwood forests in the lower Mississippi River Valley, the Okefenokee Swamp on the Georgia-Florida border and mangrove forests in Florida Bay. There are also swamps in tropical Africa, South America, and Southeast Asia. In the past 100 years, hundreds of welands have been destroyed across the U.S. to make room for farmlands, roads, and housing property.