If you want to leave a message to me on any issue relating to Commons, or Commons-hosted imagery please leave it here. Please only leave messages on my en.wikipedia talk page if it is strictly an en.wikipedia matter.
That's the result of limitations in my workflow. The river data is from OS Meridian 2, which for the most part, labels the rivers. To maintain clarity, I remove the unlabelled sections as these are usually the minor, possibly unnamed, streams. In this case, the Ouzel from its confluence with an unnamed stream (just north of the M4 and Willen Lake) to the Ouse is not labelled so got removed. I can correct that easily enough.
Also noticed a more serious error - the headwaters of the w:River Lea in Luton are shown as an isolated river in the Great Ouse catchment, and not as part of the Thames...
Since I created that map OS has released a new Open Rivers product, which has a connected network. With any luck, that will avoid issues like these.--Nilfanion (talk) 10:50, 14 June 2015 (UTC)