I do not know the course except I have walked the length of this [approx 18 miles at varying times] from Stowmarket to Stoke Bridge, Ipswich. Some claim the Gipping ceases at The Bridge by the Railway Station, some say Stoke Bridge. I'm not an expert but the fresh water Gipping discharges into The River Orwell just past London Road Bridge in Ipswich where there is one major sluice gate followed by a smaller sluice
Some people argue that the Gipping ceases here at Stoke Bridge and then becomes the River Orwell, others proclaim that the Gipping ceases at the sluice near London Road bridge, this to me is the obvious way of determining the end as this is where fresh water discharges into the tidal river
From Gt Blakenham Lock Gates looking West you can walk to Needham Market & Stowmarket with a footpath on the left through the back of the Vicarage, the right side here is private property