| Little boys of village go to Beel for catch fish | 
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]
