The River Thames data logger above Shiplake Lock records data in an RRD database, which is periodically dumped to an XML file and archived here.
The data is open source and you are welcome to use it, but there are a few things that you need to be aware of:
# Archive periods based on 300s primary data points: # samples/entry time/entry entries archive length # 1 5m 10000 34 days # 12 1h 10000 416 days # 72 6h 15000 10 years
See also
findlays.net is run by Andrew Findlay