Beel a large surface waterbody that accumulates surface runoff water through internal drainage channels; these depressions are mostly topographic lows produced by erosions and are seen all over Bangladesh. The term beel is synonymous to baor, and familiar in greater comilla, faridpur, dhaka and pabna districts. Beels are small saucer-like depressions of a marshy character. Many of the beels dry up in the winter but during the rains expand into broad and shallow sheets of water, which may be described as fresh water lagoons.

Beels can be formed due to many causes. In some cases a string of them is found along a line of drainage, suggesting that they are the remains of some great river, which centuries ago deserted its channel in favour of a new one somewhere else. In other cases, they are probably due to the action of rivers, which by centuries of silt deposits have raised their beds and marginal banks so high that they flow above the level of the surrounding area. The land between a pair of parallel rivers thus forms a kind of trough in between. The rivers, on the other hand, cannot overflow their banks into these depressions as they themselves are locked within their channels by high levees.

In the active floodplains of the Surma-Meghna, the Brahmaputra-Jamuna, and the Ganges-Padma river systems, there are several large and small beels. In Bangladesh, there are thousands of beels of different sizes. Some of the most common names are chalan beel, gopalganj-khulna beel and arial beel. Most of these large beels have shrunk quite considerably in recent decades. For instance, in the early 19th century Chalan Beel used to cover an area of about 1,085 sq km but it was reduced to 368 sq km in 1909, of which only 85 sq km remains underwater throughout the year. It has since shrunk to only 26 sq km.

In the deeper beels nothing is to be seen but water, often dotted with chars or enclosed by high lands with villages and trees on them. Many of the villages are completely isolated during the monsoon, when the only mode of transport is a boat. Not surprisingly, these beels form a serious obstacle to transport by land as roads can be constructed across them only at a great expense. The roads again have to be strong enough to withstand the pressure of water, which may be as much as 3.05m in depth.

Beels are mainly fed by surface runoff water. A few larger ones are fed by floodwater during the wet season from the parent river channel. Regionwise, in the northwest some beels of considerable sizes are Bara Beel at pirganj, Tagrai Beel at kurigram, Lunipukur at rangpur, Bara Mirzapur Beel at narail and Keshpathar at bogra. The old river course of atrai is marked by some beels, viz Chakchaki, Sabul, Ghugri, Kanchan, Manda, Utrail, Hilna, Kumar and Shona. In the southern region, important beels are Boyra, Dakatia, Bara, Kola, Patla, Chatal and Srirampur. In the central part, Katla, Chatal, Nagarkanda, and Chanda are important beels. In eastern areas, such beels are small in size. In the northeast, beels of Haor Basin (Sylhet Basin) area merge together in the wet season appearing like vast bodies of water. Normally, beels remain deeply flooded for most of the wet season and the rims are primarily used for either boro cultivation or deepwater rice. Like baors, beels are also important wetlands and regarded as valuable fish and wildlife habitat. [Mohd Shamsul Alam and Md Sazzad Hossain]