Could someone explain this sentence a bit? Why 강은 물이?
Same use as 키가 added to 크다 (키가 크다) to mean big in height, hence tall. (*키 = height).
물이 is added to 강은 (강은 물이) to mean that it is about the river water level and not about the height of the river banks.
It's basically, "with respect to the river, is the water shallow?". That's how the topic and subject are separated but of course the water referred to is the water in the river.
"강 물이 얕습니까?" is much more natural. I report it.
I wrote that, and it is accepted as correct. Jan. 4, 2020.
강물 is accepted as it is a recognized compound noun = river-water.
But not 강 물 (with spacing).
"강의 물은 얕습니까?" was marked wrong, and my native speaking partner is not pleased. :P
똑같은 문장을 썼는데 아직 틀려요: 삼월/육일/이천이십년.