Wetlands refer to marshes, swamps, floodplains and shallow coastal areas. It is an environment where the water table is almost always near the surface. Wetlands are divided into estuarine and freshwater systems, which are further subdivided based on soil type and vegetation nature. Wetlands are characterized by slow flowing or still water and the water body is a free habitat for wild aquatic fauna.

According to the Ramsar Convention-1971, wetlands are defined as: “Natural or man-made, permanent or temporary, stagnant or flowing bodies of fresh, brackish or mixed water, swamps, marshes or wetlands, and deep marine areas that are at low tide does not exceed a depth of more than 6 meters''.

World Wetlands Day is celebrated globally on 2nd February every year. This day is observed to commemorate the signing of the Convention on Wetlands. On this day in 1971, the Wetlands Conference was held in the Iranian city of Ramsar on the shores of the Caspian Sea to highlight the international utility of wetlands. The day was celebrated globally for the first time in 1997.

Different categories of wetlands have been identified worldwide based on biological and physical characteristics, of which 30 are natural and 9 are man-made. Wetlands of Bangladesh can be classified based on hydrological characteristics, topography and environmental functions: 1. Brackish Wetlands: a) Marine: Permanent shallow bodies of water during low tides, e.g.: Gulf reefs, St. Martin reefs, b) Estuarine: Moderately vegetated intertidal mud, sand or salt flats, e.g.: newly raised land, intertidal wetlands, intertidal forested wetlands and riparian forests; c) Saline lacustrine wetlands: Fresh-saline to brackish lakes connected to the sea by narrow channels.

2. Freshwater Wetlands: a) Riverine Wetlands: Temporary seasonal rivers and streams including permanent rivers and streams and some grasslands, b) Lakes or Beel Wetlands: There are thousands of lakes of various shapes in Bangladesh. Most of them are located in Rajshahi, Pabna, Khulna, Jessore, Faridpur, Comilla, Noakhali and Sylhet districts of the main delta region, c) Palustrine Wetlands: Vegetated permanent freshwater swamps and floodplains, peat-forming permanent freshwater floodplains, freshwater floodplain forests c) Man-made wetlands: fishponds, irrigated lands and irrigation canals, salt fields, dams such as Kaptai Lake.

Soil scientists in Bangladesh have different views on the definition of wetlands from an agricultural point of view. Based on the frequency and depth of inundation, the entire country is divided into six major land types: upland, mid-upland, mid-lowland, lowland, ultra-lowland and subsoil. Within this land classification, areas of submerged soil ranging from mid-lowland to subsoil are considered wetlands. Bangladesh has a vast reservoir of wetlands consisting of numerous rivers, streams, freshwater lakes and marshes, haors, dams, canals, beels, fish ponds, flooded agricultural lands and estuarine systems with extensive riparian forests.

However, wetlands of coastal and marine origin are less important in Bangladesh. Haor, Baor, Beel, Jheel etc. of river sources are generally called freshwater wetlands. These freshwater wetlands span four landscape units – floodplains, freshwater marshes, lakes and submerged forests. Man-made wetlands include artificial lakes, and ponds. Wetlands located at the lower end of the topography are inundated by shallow to deep flooding during the monsoon season. A haor can be divided into three parts based on elevation and hydrology: mountain foothills, floodplains, and deeply flooded areas.

Wetlands of Bangladesh have a wide range of environmental, socio-cultural, economic and commercial importance and value. These wetlands of local, national and regional significance are home to numerous biodiverse flora and fauna. Wetlands of Bangladesh are very important for human settlement, biodiversity, fishery production, agricultural diversification, navigation and communication and eco-tourism etc.

More than five thousand flowering plants and 1,500 species of vertebrates including about 750 species of birds and 500 species of coastal estuaries and freshwater fishes are found in the wetlands of Bangladesh. About 400 species of vertebrates and about 300 species of plants depend on wetlands for part or all of their lives. About 260 species of freshwater fish are found in the wetlands of Bangladesh. Freshwater fishing is an important source of livelihood and also one of the main sources of animal protein.

In the last three decades, extensive physical infrastructure development has been achieved in wetlands and floodplains and haor areas such as roads, flood control dams, etc. Ignoring the local topography and natural water flow during most of the development activities has resulted in poor quality drainage systems and water logging and its impact on local surface water bodies is also observed. Such development activities are rapidly transforming wetlands on a massive scale. Due to human intervention in wetlands, the country's ecosystems are constantly being destroyed and the long-term sustainability of wetlands is threatened.

For example, in the brackish water-rich lands of the southwestern coastal plain of Bangladesh, farmers would cultivate paddy when monsoon rains removed the salinity from the soil. This farming system has been going on for centuries. But for the past two decades, this practice of farming has been abandoned and instead, shrimp farming is being done to gain more profit. As a result, local ecosystems are on the verge of collapse due to altered water exchange systems, sediment accumulation in riverbeds and constant inundation of land with saline water.

People from surrounding densely populated areas are settling in haor areas and this is causing adverse reactions. Continued massive extraction of aquatic plants and fruits such as: makna, singara, padma, shapla, hogla etc. has severely reduced both the quantity and quality of these plants required for fish and guest bird habitat in haor area. Similarly, dams built for flood control and irrigation projects not only reduce the floodplain but also obstruct the movement of tributaries from the river to the floodplain. As a result, many fishermen are forced to give up their livelihood.

​Wetland conversion also has some positive effects. The main influence is on the type of cultivation. As a result, dependence on local boro rice has decreased and dependence on high yielding boro rice has increased. Fish farming in flood control and irrigation project areas is helping to meet the deficit in natural fisheries. Improved road transport and communication systems have improved marketing infrastructure and social and other services have become relatively accessible in positive response to development projects in wetland areas.

Degradation of wetlands has created many problems. These include - extinction or critical decline of several wildlife species including birds and reptiles, extinction of many native rice varieties, destruction of many native aquatic plants, and shrubs, depletion of natural nutrients in soil, natural water bodies and those derived from them, loss of benefits, increased incidence of flooding, destruction of wetland-based ecosystems and dissolution of socio-economic institutions and culture, and above all disruption of human livelihoods. Dynamic ecosystems of wetlands change over time to time. However, any modification of wetlands through human activities must be managed with caution.