The marshy inlet of a river or lake is called a bayou. The name for an artificial waterway is a canal.
I am not sure of the answer but it is not a delta since a delta need not be marshy and the question asks about marshy land.
Bayou
marshy plain near the river, and dry forest and thorny scrub elsewhere marshy plain near the river, and dry forest and thorny scrub elsewhere
low, marshy ground = bog or swamp
Cause they are marshey, and they're birds.
The Nile River Delta.
a delta
bayou
Nubia is the marshy part of the Nile near the Mediterranean sea.
bayou
A bayou is a marshy creek or swampy backwater of a river or lake. They are very common in the U. S. along the gulf coast.