It could have just been overflow water at flood time, but the main flow of the current continued to flow into the Gulf.
(It; could have just been; overflow water; T:at flood time) (the main flow of the current; continued; ) (the main flow of the current; to flow; into the Gulf)
It the main flow of the current the main flow of the current
could have just been continued to flow
overflow water T:at flood time
into the Gulf