Below are a variety of sites to get information on what is happening with the river that you may find them useful.
https://flood-warning-information.service.gov.uk/station/7172 This shows the up to date river levels both upstream and downstream of Old Windsor Lock. This is probably the most useful link.
https://www.gov.uk/sign-up-for-flood-warnings As it says, this is where you can sign up for flood warnings.
https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=498342.81&northing=174610&map=SurfaceWater This one gives all sorts of flood risks, just enter your postcode and what type of risk you are interested in.
https://flood-map-for-planning.service.gov.uk/confirm-location?easting=498478.53&northing=174647.94&placeOrPostcode=old%20windsor A great one for planning and showing the flood zones.
https://flood-warning-information.service.gov.uk/5-day-flood-risk This one gives a basic 5 day flood risk.