They say, Wetlands are known as the earth's 'kidneys' because, like your kidneys, they serve the very important function of filtering water. As water moves through a wetland, the sediments and pollutants 'stick' in the wetland, making the water cleaner. Wetlands also help reduce flooding and prevent shoreline erosion. provide vital habitat to a number of species, including (but certainly not limited to) waterfowl, wading birds, frogs and salamanders, aquatic invertebrates, turtles, and fish. They also provide a number of essential ecosystem services like purifying our water, absorbing flood waters, and protecting coastal and riparian areas against erosion and highly productive environments that support biodiversity and provide vital ecosystem services. Wetlands protect against flooding, filter contaminants and excess nutrients, stabilize shorelines, refresh groundwater supplies, and help regulate earth's climate, while lessons learned from natural ecosystems can be used to engineer more effective constructed wetlands.

Wetlands may be natural or human-made. The only continent on Earth that does not contain natural wetlands is Antarctica. Human-made wetlands may be constructed for water management purposes in urban areas. What is unique about all wetlands is that they contain vegetation that is specially adapted to such wet conditions. Plants that live in wetlands must be quite tolerant of wet, productive soils.

There are four main types of wetlands based on their location, water salinity, and dominant vegetation.

Marshes are wetlands that are usually permanently saturated and can be saline or freshwater. Marshes can be tidal or non-tidal. Tidal marshes occur along coastlines and are affected by changing tides, while non-tidal marshes occur along streams. Tidal marshes are often brackish or saline, and the vegetation found in this type of wetland is adapted to both wet and salty conditions. Non-tidal marshes are usually freshwater but can also be brackish. Non-tidal marshes are the most common wetland in North America.

Swamps are freshwater wetlands that are dominated by woody plants. There are many different types of swamps, and they become saturated with freshwater from stream and river runoff. The easily recognizable cypress tree is found in forested swamps.

https://study.com/academy/lesson/what-are-wetlands-definition-types-quiz.html

http://www.wildlifehc.org/celebrate-world-wetlands-day-on-february-2/

https://uwaterloo.ca/ecohydrology/world-wetlands-day/world-wetlands-day-2017