Toward the back, around the river, it's salty (8)
I believe the answer is:
brackish
'salty' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for brackish that I've seen before include "rather salty" , "Rich bask in slightly salty water" , "Somewhat salty" , "unpalatable" , "Sightly salty, as water in estuaries" .)