The Environment Agency charged the water company with letting potent amounts of suspended solids and iron into the River Test near Stockbridge in March 2023.
The firm also didn’t alert the Environment Agency when it became aware of the issue or about the failing equipment that caused the incident.
Southern Water pleaded guilty to two charges relating to environmental permit breaches at Medway Magistrates Court on 14 July 2026. Sentencing will take place at a later date.
Simon Moody of the Environment Agency said
Chalk streams like the River Test are precious, natural resources. But they are also fragile and this incident came to light thanks to the close eye we keep on their health.
Southern Water’s safeguards which should have protected this chalk stream failed one by one. That’s unacceptable. Chalk streams should be gin clear. Thorough maintenance and tested process would have prevented this.
The River Test became discoloured downstream from the Southern Water wastewater treatment works
The Environment Agency was doing routine water quality checking of the River Test at Stockbridge, Hampshire, on 13 March 2023 when dark particles were found in the water. The colour and intensity of this matter grew thicker as sampling followed the trail upstream.
The Environment Agency found the source nearly 4 miles upstream from where it was first noticed. It was a dark plume from Southern Water’s Fullerton wastewater treatments works.
Southern Water site staff said only one of the four tanks used to remove sludge and scum was working properly. One had been awaiting repair for over a year.
The pumps which sent effluent to deep, sand beds to filter away finer contaminants and solids also had problems. The site diary confirmed the technical issues had been logged days earlier.
Salmon born within the River Test chalk stream are genetically unique. They are more vulnerable and less resilient than other salmon and need clean, well oxygenated water.
The discolouration, which had a reddish tinge, stretched across half of the chalk stream’s width
Sampling confirmed the level of suspended solids in the water was over triple the permitted limit. The amount of iron in the water, giving the pollution a red tinge, was also much higher than the allowed amount from the treatment works.
After the incident, Southern Water noted it had missed at least two opportunities to alert the Environment Agency. Its procedures hadn’t been followed
Southern Water said it recognised the procedure for raising concerns internally and to the Environment Agency about the quality of the treated effluent going into the River Test had failed before and on the day of the incident.
Sampling on 24 March – 11 days after the Environment Agency acted – confirmed the water quality was much improved.
This year the Environment Agency hit its inspection target of 10,000 water company assets. This included over 730 checks of Southern Water sites, 68% of which were found to be compliant with their permits. Officers gave Southern Water over 400 improvement actions off the back of their inspections.
Background
Southern Water pleaded guilty to two charges put to it by the Environment Agency at Medway Magistrates Court on 14 July 2026. Two other charges will be taken into consideration at sentencing, date to be set.
The charges are
Charge 1. On 13 March 2023 at Fullerton Wastewater Treatment Works contravened condition 3.1.1 and Table S3.1(a) of Environmental Permit number A.804/H/07/V003 in that a discharge from the works contained more than 50 milligrammes per litre (mg/l) of suspended solids, contrary to Regulation 38(2) of the Environmental Permitting (England and Wales) Regulations 2016.
Charge 2. On 13 March 2023 at Fullerton Wastewater Treatment Works contravened condition 3.1.1 and Table S3.1(a) of Environmental Permit number A.804/H/07/V003 in that a discharge from the works contained more than 8,000 micrograms per litre (ug/l) of total iron as Fe, contrary to Regulation 38(2) of the Environmental Permitting (England and Wales) Regulations 2016.