How is an oxbow lake formed?
a.
an oxbow lake is formed when a lake shrinks due to erosion.
b.
an oxbow lake is formed when the wide bend of a river is cut off.
c.
an oxbow lake is formed when high concentrations of salt are present in lakes.
d.
an oxbow lake is formed when a dam or levee is built on a river.

After a long period of time, the meander becomes very curved, and eventually the neck of the meander becomes narrower and the river cuts through the neck during a flood, cutting off the meander and forming an oxbow lake. ... When deposition finally seals off the cutoff from the river channel, an oxbow lake is formed.    An oxbow lake is formed when the wide bend of a river is cut off.      

Its decreasing because of illnesses