Rivers and Seas Watch FAQ

During heavy rain, local sewer networks can struggle to cope with the amount of water entering pipes and storage tanks.

When they fill up, we use pressure relief valves built into the network – known as storm overflows – to stop homes and businesses from flooding. These overflows release excess water through outfalls into rivers and the sea. Storm overflows are part of the design of the sewers and are regulated by the Environment Agency. They're used in areas where the sewers were built to carry both wastewater from homes and businesses, and rainwater from roofs, gardens and roads.

Storm overflows can have an impact on water quality, however there are many other contributing factors including agricultural runoff, seabird and animal matter and marine activity.

Because of these other factors, Southern Water can’t advise about water quality and whether it’s safe to swim. We can only make predictions about water quality impact caused by storm overflow releases.

Rivers and Seas Watch consists of three main features, the map, the historic release table, and the information page. You can also sign up for email updates or send us feedback using the buttons at the top of the screen.

Icons and legend
Each of our storm overflow outfalls is represented with a circle, and our region’s designated bathing waters are represented with a location pin.

The bathing water pins act as an umbrella, containing all outfalls that are associated with it. If one outfall associated with the bathing water is showing as red, its associated bathing water pin(s) will also be red. Some outfalls are associated with more than one bathing site; if a release from an outfall can impact the bathing site, then that outfall would be classed as associated with it.

Red: Release(s) in the last 24 hours
Amber: Release(s) in the last 72 hours
Green: No releases within the last 72 hours
Grey: Under maintenance

Map
To use the map simply locate the area or bathing site you’re interested in by zooming in or using the search bar, then;

• Click on an outfall circle to see details of any recent releases, the bathing water(s) the outfall is associated with, and navigation to the historic release table.
• Click on a bathing water pin to see details of any recent releases associated with that bathing water, the outfall(s) associated with the bathing water, and navigation to the historic release table.

Release table
Our Rivers and Seas Watch release table allows historic releases to be filtered by date, bathing site, outfall, status and impact, you can also customise the table columns to your liking. We believe in transparency and sharing of data, so we included the option to download results from the release table to a spreadsheet using the ‘actions’ button.

To see our annual storm release data, you can visit our Flow and Spill reporting pages.

Information page
The information page is full of helpful resources and information on Rivers and Seas Watch and storm overflows. This includes videos, frequently asked questions and deep dives on topics like tidal modelling.

We use sensors in our storm overflow outfalls called Event Duration Monitors or EDMs for short. Data from these sensors is processed through a number of applications to understand if there was a genuine storm overflow release or a false alarm, as well as what time the release occurred and for how long.

Manual checks are carried out by our analyst teams to make sure that the data is as accurate as possible. If we’re looking into a release and its validity, the icon will turn white until we’ve finished investigating, at which point the colour will change to show if there has been a release or not. The data shown on Rivers and Seas Watch is the same data that we share with our official regulators. At Southern Water we believe in open access to data to ensure transparency, and accountability for improvements.

We use tidal modelling* to work out what will happen to a storm overflow release once it comes out of the outfall and hits the water, and what bathing sites it could impact. If an outfall has the potential to impact a bathing water when it releases, then it's deemed an associated outfall. Outfalls can be associated with more than one bathing water, this is because the tide and wind conditions can push the storm overflow release in different directions.

* Tidal modelling predicts storm overflow behaviour, factoring in wind, tide strength, and direction. Validated with survey data and dye tests, our models mimic real-world scenarios, ensuring accurate performance in predicting movement and dispersion.

We use Tidal modelling* to determine the impact a storm release has on bathing water. It uses the location of the outfall, the duration of the release and tidal conditions at the time to calculate the changes of impact.

For instance, if the outfall is 5km out to sea, the release was short, and the tidal conditions indicate there could be no impact on bathing water, the bathing water pin will be blue to indicate no impact, and the outfall icon will turn red to indicate a recent release. Details about the release are shown in the bathing water pin pop up, and in the Rivers and Seas Watch release table.

* Tidal modelling predicts storm overflow behaviour, factoring in wind, tide strength, and direction. Validated with survey data and dye tests, our models mimic real-world scenarios, ensuring accurate performance in predicting movement and dispersion.

The data received from our sensors is sent to an automated analysis system where several factors are taken into consideration to determine the accuracy of the data. We carry out manual investigations when the data from the sensors isn’t clear enough for an automated decision, and events are regularly checked for accuracy.

Genuine: after review, we can confirm there is/was a release

Genuine non-impacting: after review, we can confirm there is/was a release, but our tidal modelling determined that it isn’t/didn’t impact the bathing water

Non-genuine: after review, we can confirm there was a false alarm, no release happened at this time. False alarms can happen for several reasons including disruption by wildlife, fault to the senor, manual error or power supply issues

Yes, simply click 'subscribe’ at the top of the map to sign up for email updates. You can sign up for updates on just one bathing site, or multiple sites. We'll then notify you via email if there has been an impacting storm overflow release at the site(s) you've subscribed for. You can unsubscribe at any time.

We want to make sure that Rivers and Seas Watch offers transparent data and provides the information the public wants in a clear and meaningful way. To do this, we actively listen and seek feedback from our Rivers and Seas Watch Working Group. This group is made up of local authorities, campaign groups, bathing water users and interested stakeholders, who advise us on improvements we need to make. Changes to the site are presented to the group for feedback, before changes are made.

We also survey Rivers and Seas Watch users and hold independent reviews to understand what users would like to see and how they wish to use the service. This has been a critical process in developing Rivers and Seas Watch, and we’ll continue to assess and improve the platform as time goes on.