Above is a picture of Iffley lock. Visible are the Stoney Weir (see below) and the path continues to the right to the main weir. Also visible is a red "Caution strong stream" board. This is reflected in the list of boards on the Environment Agency website.
The Stoney Weir. You can see the large grey counterweight in the centre of the picture. On the left hand edge of this is an indicator which shows how much it is open. It is marked up to 0.3, but it can be opened well beyond this in high stream conditions (the counterweight will be lower down the more open the weir).
The Stoney Weir indicator. You can see 4 lines; 0.0 (closed), 0.1, 0.2 and 0.3. In this picture it is open to about 0.5.
0.2 on the scale is roughly 0.5 bucks, and each additional 0.1 on the scale is another 0.5 bucks.
Continue down the path towards Iffley Village, and you will arrive at:
This is the main weir, which takes most of the flow. It comprises 6 "bucks" (sluices that can open and close) and two sets of "sticks" which can be removed and replaced.
Here you can see the 6 bucks, which will be opened to allow more water to flow through. They are all open in this picture.
Closeup of a single buck. This one is open.
At the far end are the sticks. In this picture, half the sticks are present and half are removed to allow more water to flow. The removed sticks can be seen leaning against the fence. In total the two sets of sticks account for approximately 0.5 of a buck.
The weir as pictured reads as follows:
Total:7.75, i.e. well into red flag territory.