Fishy water? Helper on the way (2-6)
I believe the answer is:
co-driver
'helper on the way' is the definition.
(someone helping a driver on a road or way)
'fishy water?' is the wordplay.
'fishy' becomes 'cod' (type of fish).
'water?' becomes 'river' (river is a kind of water).
'cod'+'river'='CO-DRIVER'
(Other definitions for co-driver that I've seen before include "Divorcer (anag.)" , "Rally partner" , "Rallying partner" .)