But it can be some what difficult to navigate through its web site to find the desired river level (for example - the river Ock is found at https://flood-warning-information.service.gov.uk/station/7081).
The Environment Agency has now made this data publicly available and data mining and mapping company Shoothill (http://www.shoothill.com/) has taken it and produced an interactive map of live data of the river levels in England & Wales: http://www.gaugemap.co.uk/#!Map
Not only is this data available on their web site, but river level updates are available via twitter and can have widgets which can be embedded into web sites (such as the Ock widget, now in the panel on the right hand side).
The river levels can also be followed on Twitter and Facebook - which not only give the river levels, but any flood alerts too.
The widgets for three rivers in Abingdon are embedded below:
River Ock (Tesco Weir)
Thames (Abingdon Lock):