The right bank from Culham Old Bridge, opposite Abingdon Marina, to Abingdon Lock and on to this point is Andersey Island, between the Swift Ditch and the main channel.


The Swift Ditch is now a weir stream leaving on the RIGHT bank above the lock. It was at one time the main stream.
955-963: Ethelwolde made the cut which is now the main navigation (according to Leland 1535)
1060:  Oxford Petition to make the new stream the main navigation.
1535:  Leland –

The chefe stream of Isis ran afore betwixt Andersey Isle and Culneham, even where now the south End is of Culneham.
Ethelwolde, Abbate of Abbingdon, and after Bishop of Winchestre, yn King Edgares days - caused - a Gut to cum out of Isis by force to serve and purge thofficis of thabbay.

[ Which being translated means that the beautiful course of the Thames at Abingdon, and that lovely bridge, were all accidentally created because a medieval Abbot wanted a flushing lavatory! The monks would then have used this new stream to transport goods to and from the abbey. ]

1577:  William Harrison,  Description of England -

No part [of the Thames] at the first came so neere the towne as it doth now, till a branch thereof was led thither from the maine streame, thorough the industrie of the monks.

1624:  Swift Ditch reopened as main navigation
1790:  Main Navigation restored to the Abingdon Stream.

1859: The Thames, Mr & Mrs Hall

About half a mile [above] Abingdon the Thames divides into two parts, the eastern portion leaving the main stream at right angles, and going to Culham Bridge, and the western going to Abingdon; the eastern part was the navigable stream from Oxford to London in the time of James I., and the old lock is still remaining, but blocked up. 'We have already quoted an extract from "The Chronicon" relating to the eastern part; and the following, relating to the western, occurs at the commencement of the volume: —
"Mons Abbendone ad septeutrionalem[sic] [sepemtrionalem?] plagam Tamese fluvii, ubi praetermeat pontem Oxenefordis urbis situs est; a quo monasterio non longe posito idem nomen inditum."

[ Translation from the difficult Latin probably written in 1117:
"Abingdon hill is on the north shore of the River Thames, where it passes by the Oxford town bridge, and from the hill the same name is given to the monastery positioned close by."
I think dune was an upland area, the monastery got its name from the Abing dune, - a large area between what is now Abingdon, and Oxford, and the town then got its name from the monastery. (Maybe)
Mr & Mrs Hall seem to think that the bridge referred to is Abingdon Bridge and that therefore this is a reference to the western of the two streams.