The opposite of shallow is deep.
shoal
lagoon
I always stick to the shallow end of the pool.The bath was shallow.He was always a shallow person.
TREADING
wade
From the root word "lunod" which means "drown", "drowning'' in tagalog is equivalent to the word "nalulunod".Tagalog Translation of DROWNING: nalulunod
Shallow is an adjective.
Flats
There is no such word in English.Perhaps you are thinking of the word "ditch" which is a shallow channel dug to carry surface water away.
The answer is Creek.
Paddle Wade