BBC analysis suggests more than 76,000 sewage spills recorded in Scotland after new monitors installed

The new monitors, added to waste overflow sites across the country, have revealed tens of thousands of spills that would previously have gone unrecorded, including hundreds at beauty spots such as Loch Lomond. The data shows more than 100,000 spills totalling almost 277,000 hours were recorded last year, an average of about 274 a day.

Sewage spills occur automatically at overflow sites, which are designed to release excess water into natural waterways during heavy rainfall to prevent flooding into homes, businesses and streets. Scottish Water currently has over 4,200 overflows across its network, with the number of monitored overflows rising from 273 to 1,275 in 2024.

Scottish Water figures show Glasgow's River Clyde was one of the most impacted waterways, receiving almost 6,150 spills last year, or the equivalent of 17 a day. When adding in the Clyde Estuary, Firth of Clyde and other unnamed tributaries, this almost doubles to nearly 14,200 spills, or 39 a day. The Clyde Estuary also recorded the longest duration of spills at more than 25,000 hours, followed by the River Clyde with more than 15,000 hours.

Barcloy Mill Burn in Dumfries and Galloway, a newly-monitored site, received the most spills last year with almost 3,500. The data suggests 225 sites recorded no spills and 525 recorded fewer than 10. There may also be errors which suggest a monitor is active when it is not. Just under 12% of overflows are legally required to report their data to the Scottish Environment Protection Agency (Sepa), which said it has a "risk-based approach" prioritising areas for monitoring based on population and environmental need. None of the new monitors were required to be reported to Sepa.

Scottish Water said the vast majority of spills are not harmful to the environment. Simon Parsons, director for wastewater, said most of the time overflows do the job they are designed for, draining rainwater out of the sewer system. "The vast majority of those spills aren't harmful to the environment because they're nearly always about rainwater," he said. Scottish Water said 99% of spills were rainwater, surface water, road run-off, "grey" water from households (not human waste), infiltration of groundwater, and trade effluent.

Parsons said the increased monitoring had improved understanding of the sewer network and helped identify locations requiring improvement. "We didn't necessarily know how and when our overflows were operating so we've got a much better picture now than we've ever had before," he said. "We can actually identify those areas where we need to think about investment."

Local campaigner Ruth Plevin, a member of the River Almond Action Group, said she wants the group's legacy to be clean, safe water. "It's what's not visible that is our concern – the microplastics, the pharmaceuticals, the agrichemicals, stuff that you can't see," she said. "I want it to be clean – it's not a lot to ask for, really."

At Belhaven in East Lothian, surfer Brian Allen, regional representative for Surfers Against Sewage, has been testing local water for E.coli and intestinal enterococci. He said 86% of samples were rated as excellent, good or sufficient water quality, with 77% coming back as excellent. "What we don't know is whether that picture is being replicated across the rest of Scotland," he said.

Monitoring in Scotland remains far lower than in England, which has 100% coverage. Differences in recording mean Scotland's figures are not directly comparable with the rest of the UK. Scottish Water said its monitoring had now grown to about 50% and it aims to reach 100% over the next five to six years.