(Original photo copyright Historic England)
That looks more like a very old cutting for the ‘Thames’ through to Port Meadow.
So ‘The Isis’ is only from there onwards until it re-joins at Sandford?
“This is partly due to the old name for the Thames – Tamesis – and because a 14th century monk, Ranulphus Higden, described the river as being a combination of two tributaries, Thama and Ysa. ”
“The Norman conquest of England was the 11th century invasion and occupation of England by an army of Norman, Breton, and French soldiers led by Duke William II of Normandy, later styled as William the Conqueror.”
King’s 0.77 (2’6″)
Godstow 1.57 (5’2″)
Saxton’s map of England, 1574