Beachgoers in Sussex were urged to avoid entering the sea at a specific section of coastline after untreated wastewater entered the water.
Warning signs were erected at Littlehampton beach on Sunday, August 30, following the discharge incident.
The pollution notification originated from Southern Water, which informed Arun District Council about the situation.
The discharge occurred approximately five kilometres offshore near Littlehampton and Climping, as well as at the confluence of the River Arun.
Subsequent investigations revealed the incident stemmed from a malfunctioning valve at one of the company’s pumping stations.
Testing confirmed the water quality subsequently improved to an acceptable standard.
The water company explained that the discharge followed exceptionally heavy rainfall on Saturday night, August 29, when Littlehampton experienced precipitation levels equivalent to 5.4 times the typical daily August average.
The storm overflow system activated to safeguard residential properties, educational establishments and commercial premises from flooding.
Simultaneously, engineers conducting repair work at a pumping station encountered mechanical difficulties with a valve that could not be fully opened, resulting in an additional release of wastewater.
Given the potential environmental consequences, the company immediately classified the occurrence as an incident and implemented measures to address the situation.
The response involved deploying specialist engineers to the affected pumping station and positioning a fleet of 50 tanker vehicles in the vicinity to manage flows if required.
Temporary overland pipelines were established to circumvent the faulty valve, supplementary operational teams were assembled and environmental assessments were carried out throughout the night.
By the following morning, the valve had been successfully opened, allowing the tanker fleet and temporary pipeline infrastructure to be stood down.
Storm overflow mechanisms function as emergency release points designed to prevent sewage backups into properties when drainage systems become overloaded during periods of intense precipitation.
These systems have attracted substantial scrutiny due to their tendency to contaminate waterways, coastal environments and ecologically sensitive zones.
Earlier this year, a Channel 4 documentary drama examined the role of water utilities in wastewater pollution, documenting accounts from individuals who maintain their health and livelihoods have been adversely affected by contaminated waters.
The water company emphasised its commitment to improving river and coastal water quality across its operational region, identifying the reduction of storm overflow activations as a key priority.
The organisation acknowledged that current usage levels and associated environmental impacts are unsatisfactory and pledged continued efforts to address the issue.
Its £1.5 billion Clean Rivers and Seas initiative has already demonstrated results, preventing more than 700 overflow incidents during its initial year of operation.
The company indicated these figures evidence the effectiveness of its strategy and stated plans to expand resources, accelerate infrastructure projects and develop additional collaborative partnerships to achieve further improvements.
The incident occurred amid ongoing scrutiny of Southern Water’s environmental stewardship.
In March, the Environment Agency conducted 730 inspections of the company’s wastewater infrastructure and identified deficiencies in maintenance practices.
The regulatory body directed the company to implement 400 corrective actions.
Southern Water reported that its improvement programme, introduced in April 2023, had achieved substantial progress by spring 2025, noting that the majority of required measures related to relatively minor technical breaches.
The company cited various performance improvements, including a 30 per cent reduction in overall pollution incidents, a 40 per cent decrease in internal sewer flooding occurrences and an 18.5 per cent reduction in water leakage levels.