Diageo’s Toxic Spill Hits a Pristine River in Scottish Whisky Country

The River Spey in northeastern Scotland is one of the world’s most pristine bodies of water. Stretching across 107 miles, it teems with salmon and trout, supporting communities built on tourism along its shores. Earlier this year, a toxic chemical spill into a critical spawning tributary killed thousands of fish and other wildlife, blighting fishing in the area for decades.

The culprit: Caustic soda from a Johnnie Walker whisky distillery owned by Diageo Plc just meters from the Knockando Burn tributary. The scale of wildlife killed was the worst in decades, said early responders to the late-April incident.

“It’s a complete wipe out,” Edward Mountain, a former member of the Scottish Parliament who’s on the Spey Fishery Board, said in an interview. “To get all that back it’s not going to take one year or two years. It’s going to take probably tens of years.”

The Scottish Environment Protection Agency is investigating Diageo and how such a vast amount of caustic soda — a powerful chemical used to clean out copper stills and pipes at distilleries — ended up in the river, according to people familiar with the matter who declined to be named discussing an ongoing probe.

“We are working closely with the Scottish Environmental Protection Agency following this deeply regrettable incident,” a spokesperson for Diageo told Bloomberg in an emailed statement. “We are sincerely sorry for the damage caused to the local environment and the impact on river users and the wider community.” The distiller has updated its controls, is engaging with SEPA in the investigation and is discussing a long-term plan to support regeneration and restoration in the area, the spokesperson added.

SEPA declined to comment on the specifics of its investigation, saying that it is continuing “to assess the environmental impacts of the incident and work with relevant parties to ensure any appropriate action is taken to protect and restore the water environment.”

Industrial development in the Speyside region, driven by the world’s highest concentration of malt whisky distilleries, has for years presented an ecological challenge for the area. The latest incident deals a severe blow to recent conservation efforts and may send environmentalists back to the drawing board. In 2019, a bridge was installed to allow fish to swim up the river and spawn, bypassing a dam built by another company’s distillery that had blocked their path. Sadly for those efforts, the latest spill happened further up in the river and killed wildlife downstream.

Diageo’s Cardhu distillery in Knockando is more than a century old and is one of four main producers in Scotland for Johnnie Walker whisky — the company’s flagship whisky brand and the world’s best-selling Scotch by volume.

For the world’s biggest spirits company, the investigation comes at a fraught time. The global alcohol industry has been hit hard as health concerns and cost-of-living pressures are putting consumers off drinking in critical markets like the US and Europe, forcing companies to cut costs and production. Diageo has already eliminated about 2,000 roles worldwide, or 6% of its workforce. Cardhu is among the sites at risk of job cuts, according to union GMB Scotland.

April’s incident at Cardhu occurred when a valve was inadvertently left open, allowing the cleaning agent to flow directly into the water, the people said. The extensive damage to wildlife across Knockando burn means that this was no small leak, they said, adding that the small size of the waterway increased the concentration of caustic soda and made it particularly deadly. The spill is estimated to have killed as many as 3,000 creatures across more than a mile, including salmon, trout, eels, invertebrates and frogs, said people involved in the response.

If Diageo is held responsible, the regulator could fine it up to £40,000 ($53,000), and even refer the case for possible criminal charges. If prosecuted, it could face a much higher fine and imprisonment for individuals found responsible under Scottish environmental laws. SEPA declined to comment on potential actions, saying appropriate measures will be taken once the investigation is complete.

The Spey is home to freshwater pearl mussels, Atlantic salmon and sea lampreys, all of which are legally protected. It’s also a fishing paradise. Angling along the River Spey is so renowned that it even has its own technique, dubbed “Spey casting” — a fly-fishing method that eliminates the use of a back-cast in places where trees and other obstacles restrict space behind an angler.

Following the spill, it could take more than 20 years for the fish stock to return to baseline levels because the entire food chain has been hit, including some invertebrates, fisheries experts said.

Even before the latest incident, the Atlantic salmon population in Scotland had been “in crisis,” with the number of wild fish falling 70% from about one million in the 1970s, a spokesperson for the Atlantic Salmon Trust said. Salmon “require simple ingredients to thrive — cold, clean water in our rivers, and protection from threats around our coast and at sea,” the spokesperson said. “Pollution in rivers is a major threat.”

Caustic soda, or sodium hydroxide, is an alkaline substance used in alcohol production to strip stills and pipes of remaining microbes after brewing. It’s extremely corrosive and upon direct contact with the skin can cause irritation or even chemical burns. When handled properly, it’s a common heavy-duty cleaner across industries, and has multiple other uses such as strengthening fabric or de-bittering foods like olives.

After its industrial use, caustic soda is supposed to be collected by authorized waste management firms that treat the chemical elsewhere. When it lands in waterways, it can devastate wildlife. Studies show that caustic soda can burns fish gills and skin, while higher concentrations are fatal.

The Speyside region is no stranger to environmental disasters. In 2014, an accidental release of caustic soda from a distillery — not owned by Diageo — into the Cromdale Burn killed an estimated 14,000 salmonids, as well as numerous eels, along a stretch of just over a mile, the Spey Fishery Board said at the time.

In a separate case, Pernod Ricard SA’s Chivas Brothers agreed to pay £10,000 to environmental groups and £9,600 to cover SEPA’s costs for discharging up to 300 liters of oil into the River Isla at its Glen Keith Distillery in Speyside in 2018. Pernod had no comment on the incident.

In 2022, William Grant & Sons — the maker of the Balvenie whisky and Hendrick’s gin — offered £12,000 to the Spey Foundation and £2,500 to SEPA to cover costs of cleaning up fermented liquid that seeped from its Glenfiddich distillery in Dufftown into the river. The leak created a “sewage fungus” stretching nearly a mile that harmed invertebrates, although no fish were recorded as having been killed. William Grant had no comment.

A Highland company was fined £32,000 in October for progressively filling a former pond with waste between 2018 and 2024, in what is SEPA’s biggest such publicly disclosed fine. One of the biggest SEPA-investigated criminal fines of £200,000 was levied against waste-management company Doonin Plant in 2012 for illegally dumping hundreds of tons of waste into a former colliery. Doonin has since gone into liquidation.

The regulator substantiated 22% pollution reports out of almost 18,000 total incidents between July 2022 and September 2025, and assessed only 118 financial penalties in that period, The Herald reported.

Scottish environmental fines pale in comparison to ones in England. In 2021, a record £90 million penalty was leveled against Southern Water for illegally discharging sewage into the rivers and coastal waters of Kent, Sussex and Hampshire.

Calls are growing for harsher fines on polluters in Scotland. Even at the top end, fines in Scotland “won’t touch the edge of the glass for some of these companies,” said Mountain.

Last year, Labour politician Monica Lennon introduced a bill in the Scottish Parliament calling for higher penalties — unlimited fines and up to 20 years in prison. The “Ecocide” bill, however, fell through after it was deemed that there wasn’t enough time for scrutiny before parliament dissolved.

For residents in Speyside, the Diageo spill is a grim reminder of a problem that’s dogged the area for years.

“You kind of say, the first time can be a mistake, the second time is not a mistake, the third time people aren’t learning,” said Mountain, alluding to the series of caustic soda pollution incidents across the region over the years. “I absolutely understand why it needs to be used to clear out pipes, but if we can’t control it, we shouldn’t be using it.”

Top photograph: Angling along the River Spey in Scotland is so renowned that it even has its own technique, dubbed “Spey casting;” photo credit: Matthew Lloyd/Bloomberg