At first the navigation remained open, but as more and more pollution appeared a boom was necessary to prevent the pollution spreading, Keith Gudgin tells us.
Oily sheen
The stoppage is at Blakes Lock in Reading, and an oily sheen can be seen around the area with the oil drifting into the Thames, hence the boom to stop it becoming polluted.
There is no intimation when the boom will be removed, so of course there is no access to or from the Kennet & Avon to the Thames.
UPDATE
The spillages was cleared up yesterday, Sunday, and the waterway is now open again.