There are some questions we get asked more often than others. This page is an attempt to answer the most common.
What does the displayed level mean in terms of actual river depth?
We don't know, and have no way of knowing. For most normal river levels, the zero point is taken from a nominal river bed height, so the gauge level does approximate to the depth. But, of course, river beds are not flat, so in some cases the displayed level will be less than the actual depth, and in some cases it will be more. See also the next question related to negative values.
The primary reason for this site is to allow people to check whether river levels are within normal bounds, or whether they are in danger of causing localised flooding. If you need to know the depth of the water for other purposes, including boating, fishing and swimming, then you will also need local knowledge that we simply don't have.
How can you have a negative river level?
There are two types of monitoring station where values can routinely be negative. The first is monitoring stations on tidal waters, where the zero level is measured from mean sea level rather than the river bed. Levels below mean sea level will, therefore be negative.
The second is reservoir and lake levels. The zero point on these is typically a nominal "normal" level, with anything below it being negative and anything above it being positive. For reservoirs in particular, there is often no red or yellow (warning or alert) section on the level graph, as the upper value is simply the point at which the reservoir overflows into the relief channels.
Why haven't you had any data from (whatever) monitoring station recently?
Usually, because it's broken. Level gauges are mechanical devices operating in a hostile environment. They can, and do, go wrong! Sometimes, data is missing from the most recent updates, and, occasionally, the data supplied is incorrect. As far as possible, we try to exclude data that is clearly wrong (eg, a water level that's so high it would indicate a flood of Biblical proportions) from the displayed graphs and calculated statistics. However, there's no easy way to account for other possible problems, such as a stuck gauge that is not correctly recording the rise and fall of a water level.
What's wrong with the values for (whatever) station? They look wrong, to me!
See above.
What's the picture at the top of the page?
That's the River Avon at Evesham, as seen from Workman Bridge. Here's a Google Streetview of it.