‘Nauseating’: Illegal sewage spills polluted protected waters, data suggests

Scottish Water illegally discharged sewage hundreds of times during dry weather, soiling beauty spots such as West Sands beach at St Andrews where the Oscar-winning film Chariots of Fire was filmed, an analysis by The Ferret suggests. 

Our investigation uncovered 2,300 ‘dry spilling’ incidents from Scottish sewers in the past five years. These spills meant wet wipes and human waste overflowed into rivers and onto beaches, even when the system was not under abnormal stress.

Scottish Water questioned The Ferret’s analysis, however, and said it does not accept that these were “dry weather discharges”. The firm also said it has invested £2.7bn in improving and maintaining the public drainage system over the past decade.

Discharging sewage during dry weather into rivers and seas is illegal. Spilling sewage that has not been fully treated is only permitted as a result of unusually intense rainfall which dilutes it. 

The Ferret discovered four per cent of sewage spills recorded between 2018 to 2022 by Scottish Water, a public company, took place when it was not raining. This included periods of drought.

Water contaminated with sewage contains bacteria and viruses that can cause stomach upsets, diarrhoea, vomiting and skin infections if people are exposed to it. Sewage spills can have lethal effects on wildlife. Spills on dry days have a higher sewage concentration and are more harmful.

Our analysis shows sewage was also spilled into protected environments. At one sewage treatment plant discharging into protected waters where shellfish thrive, raw sewage has been spilling since 2008 because the plant is unable to process the volume of sewage quickly enough.

Campaigners said our findings showed “that a nauseating level of pollution is being kept under wraps”. Surfers Against Sewage accused Scottish Water of “appalling behaviour” and called on Sepa, the Scottish environment regulator, to “stand up to the polluters“.

Alex Cole-Hamilton MSP, leader of the Scottish Liberal Democrats said that “it seems like every appalling practice adopted by the private water companies in England is being mimicked by the government-owned water company in Scotland.”

Did a dry spill take place near where you live? Click on markers for more information – zoom in to see the spill locations

To identify dry spills, The Ferret cross-referenced two data sources: Scottish Water spill records from monitored discharge pipes, and information about rainfall within 1.9 miles (three kilometres) from each spill. 

Scottish Water said that its network was designed to overflow under licenced conditions and that the spills we identified were “routine”. It does not accept that they are dry spills and does not currently correlate sewage discharges and rainfall. The company questioned whether the chosen radius covered a large enough catchment area.

Scottish Water said: “Any asset that spills in dry weather is the highest priority for investigation and intervention.” It is currently aware of 14 overflows that have spilled on dry days but none of them is monitored and does not feature in the analysed data. 

Sepa said it was clear about their role of ensuring Scottish Water reduces spills and improves water quality.

Four in five dry spills were from storm tanks – reserve capacities at sewage treatment works. Sewage discharged from storm tanks receives partial treatment but still contains faecal bacteria. 

Ninety-five per cent of sewer overflows in Scotland are not monitored, suggesting dry spilling could be significantly more extensive.

Dry spills in protected areas and during drought

The Ferret compared locations and times of spills with environmental information from Sepa. Our analysis found dry weather discharges took place in protected environments and areas suffering from water scarcity.

Two overflows spilled sewage on rainless days into protected shellfish areas. A storm overflow at Tighnabruaich sewage treatment plant, in Argyll and Bute, discharged partially treated sewage into the Kyles of Bute more than a hundred times in dry weather in 2022.

An overflow near Balvicar sewage treatment works, Argyll and Bute, discharged raw sewage 68 times on days without any rain during the past five years. Untreated sewage has been spilling from the Balvicar plant into the Seil Sound since 2008. 

Sewer overflows discharging to East and West Sands bathing waters in St Andrews spilled untreated sewage three times during dry weather in 2019 and 2020. Both beaches are popular with swimmers, surfers and holidaymakers. 

The overflows from Stevenston and Meadowhead sewage treatment works discharging to Irvine beach in Ayrshire spilled raw sewage 26 times in dry weather between 2019 and 2022. 

River Endrick, in Stirlingshire, saw 6.5 million litres of excess sewage released from Balfron and Fintry sewage treatment works on dry days between 2021 and 2022. 

In the five year period, Helensburgh and Ardoch sewage treatment works have been regularly discharging excess wastewater into the Inner Clyde – a bird reserve that is open to the public.

These dry spills are yet another shocking example of the water industry being given an inch and taking a mile.

Josh Harris, Surfers Against Sewage

Sewage has also been discharged hundreds of times into the rivers that are at risk of nitrogen and phosphorus saturation, including rivers Clyde, Ayr and Avon. The pollution can cause algal blooms – which can be toxic to wildlife – so these waters are especially sensitive to sewage spills. During dry spells in the past five years, sewage had been spilling into them for a total of 3,500 hours.

Shieldhall sewage treatment plant in Glasgow spills partially treated sewage into the Clyde estuary. During a dry eight-day period in March 2022, the Shieldhall storm tank spilled 225 million litres of undiluted sewage.

For comparison, when Scottish Water spilled two million litres of raw sewage into the Red Burn in Cumbernauld, Dunbartonshire in July 2014, a number of fish died.

In Aberdeenshire, River Ythan was dried up to its extreme low level – occurring one per cent of the time – in August and September 2022. The surrounding area was declared by Sepa to be suffering from significant water scarcity – its highest class. 

Yet the storm overflow at the Ellon sewage treatment works spilled sewage seven times into the dried-up riverbed on 10, 11, 30 and 31 August. 

Flow at river Clyde was also ‘very low’, defined as in the lowest five per cent. Yet wastewater treatment centres at Daldowie and Hamilton discharged six times a total of 2.1 million litres of partially treated sewage into the Clyde, despite the absence of rain.

Dr Linda May, ecologist from the UK Centre for Ecology and Hydrology said: “There is a higher risk to nature, and to people who come into direct contact with water, under low flow conditions because there is less water in rivers to dilute any effluent that is released into them.”


Scanty spill monitoring conceals real extent of problem

Overflows are pressure outlets on ‘combined’ sewers – underground channels collecting both sewage and rainwater into the same system. Overflows may spill as a safety measure when heavy rainfall causes the water in the channel to rise above a certain level, like a pressure hole in the bathroom sink. 

Scottish Water said dry spills can happen if the sewer is blocked or faulty. It claimed it deals with 36,000 cases of blocked sewers each year. Most are caused by non-degradable wipes, sanitary products and kitchen grease.

One in five dry spills was from regular overflows serving as pressure valves on the sewer (also called combined sewer overflows or CSOs) – and received no sewage treatment.

Campaigners and politicians fear lack of spill monitoring could mean that dry spilling is a bigger issue than indicated in the data. Dr Laura Foster, head of clean seas at Marine Conservation Society, said: “We need to see electronic monitoring of all overflows, so we know the full extent of the problem. For the sake of our rivers, seas, and our own health, we need to prevent sewage discharges.”

The vast majority of the Scottish 50,000 km sewer system – which is made of 1,800 sewage treatment works and 3,600 sewer overflows – is not monitored. 

The company currently monitors 106 overflows from sewage treatment works and 54 on the sewer network. But Scottish Water plans to monitor more than a thousand overflows by the end of 2024. They will include all bathing and shellfish protected waters.

Outlets spilling in dry weather are queued for repair by Scottish Water. The company has identified 14 sewer overflows spilling in dry weather through surveys. It refused to say which ones but none are listed as their monitored assets.

Josh Harris, head of communications at Surfers Against Sewage, a campaign group, said: “Scottish Water has a lot to answer for. These dry spills are yet another shocking example of the water industry being given an inch and taking a mile. Sepa, as the regulator, should be standing up to the polluters and demanding better for our waterways. Scottish Water should be ashamed and we stand alongside our communities across Scotland in calling out this appalling behaviour.” 

Cole-Hamilton said: “Scottish Liberal Democrats will continue to demand action to stand out dry spilling entirely. That means speeding up measures to upgrade Scotland’s Victorian sewer network, sewage discharges properly recorded and published to uncover the true scale of the problem and legally-binding targets to tackle sewage dumping.”

For the sake of our rivers, seas, and our own health, we need to prevent sewage discharges.

Dr Laura Foster, Marine Conservation Society

A Scottish Water spokesperson said: “This is a very complex area and we question the methodology and approach being used to support this analysis and the statements based on it.

“Scottish Water does not accept that these are dry weather discharges and we would not expect routine discharges to be Environmental Pollution Incidents (EPIs). These are routine discharges that are a normal, planned part of the wastewater system operation and are fully compliant with water industry regulations.

“The analysis highlights that 80 per cent of what are claimed to be dry weather discharges are from storm tanks, which partially treat waste water. This suggests there has been rainfall in the catchment since that is when storm tanks usually come into operation. It is therefore not a ‘dry weather’ event.

“The term ‘raw sewage’ is misleading – the vast majority of waste water discharged is from sinks, baths, showers, household appliances and rainwater and only about one per cent is actual toilet waste.

“The water environment is generally good in Scotland with 98 per cent of Scottish bathing waters achieving the bathing water quality standard and 87 per cent of water bodies meeting Good status or beyond for water quality.”

Nathan Critchlow-Watton, head of water and planning at Sepa said he welcomed the public interest and the “growing aspirations – heard loud and clear – for our water environment.” 

“While Scotland already enjoys some of the best water quality in Europe, Sepa is focused on ensuring improvement continues.” 

A Scottish Government spokesperson said: “We have sought reassurance from Scottish Water and we note that they have challenged representation in detail.”

They said Scottish rivers and coastal waters were already rigorously monitored by Sepa. ”This monitoring shows they are in good health.” They said the overflows can be caused by sewer blockages, which can also cause property flooding and added: “We all need to be more careful about what we flush.”

In 2020, Scottish Water pleaded guilty to polluting the River Clyde with raw sewage for a month during 2016 and was fined £19,000. The smell from the spill permeated residents’ homes and furnishings. 


Our methodology for combining spill events with rainfall data follows that used in a recent BBC investigation on dry spilling in south east England. 

Scottish Water publishes data on sewage spill events for 2018-2022. These include coordinates of the spills.

Detailed daily rainfall data for each square kilometre in the UK comes from MetOffice’s sensors. We extracted rainfall information for the time and place of each spill. We considered the weather at the overflow pipe location as dry if rainfall was below 0.25mm in a three-kilometre radius from the pipe on the day of the spill as well as three or more consecutive days preceding it. 

Download “Scottish Water sewage spills and rainfall 2018-2022”

The_Ferret_-_Scottish_Water_sewage_spills_and_rainfall_2018-2022.xlsx – Downloaded 0 times – 3.73 MB

This Ferret story was also published with the Herald. Our partnerships with other media help us reach new audiences and become more sustainable as a media co-op.  Join us to read all our stories and tell us what we should investigate next.

Leave a Reply

Your email address will not be published. Required fields are marked *

Hi! To read more you need to login.
Not a member yet? Join our co-operative now to get unlimited access.
You can join using Direct Debit, payment card or Paypal. Cancel at any time. If you are on a low-income you may be eligible for a free sponsored membership. Having trouble logging in? Try here.
Hi! To read more you need to login.
Not a member yet?
Hi! You can login using the form below.
Not registered yet?
Having trouble logging in? Try here.
Back our next investigation
Can you help us find out who really runs Scotland?