The Jubilee River is a great place to go canoeing. Though it is actually a flood relief channel for the Thames, it has been landscaped and a decade after it was opened it is now a pleasant haven for wild birds. The Jubilee River runs from just above Maidenhead to just below Eton.
The "river" actually feels more like a long thin lake, as normally the flow is very modest, even when the Thames is running high. This makes it unique amongst paddling places in the Thames Valley.
There are a number of weirs. The top 2 are not runnable and dangerous, but the lower weirs can be slid down in the right conditions. All the weirs can be portaged.