Faulty pumps caused raw sewage to spill into Windermere, England's largest lake, for about 10 hours.
The documents from United Utilities, viewed by the BBC on Wednesday, revealed that a telecoms glitch on February 28 halted the main pumps.
Emergency back-ups then took over and pumped raw sewage intermittently over 10 hours into the lake, situated in the Lake District national park, a UNESCO World Heritage site.
United Utilities manages the wastewater network in northwest England.
Windermere, renowned for its natural splendour and cultural significance, has drawn millions of visitors annually and serves as a muse for artists like William Wordsworth and Oscar Wilde.
The incident has sparked broader concerns across the UK regarding untreated sewage discharge into water bodies.
United Utilities says prompt action was taken to address the issue, attributing the mishap to an unforeseen telecommunications fault.
Normally, sewage is directed to Windermere Wastewater Treatment Works, and discharging untreated sewage into Windermere is permitted only during exceptional rainfall events.
Prime minister Rishi Sunak's spokesman condemned the sewage discharge as "completely unacceptable," emphasising the need for water companies to rectify such incidents.
The Environment Agency is conducting an investigation, with potential enforcement actions, including criminal prosecution.
Tim Farron, the Liberal Democrat party's environment spokesperson representing Windermere, denounced the event as a "scandal." He highlighted public outrage and criticised water company executives for receiving hefty bonuses amidst environmental degradation.
Windermere has grappled with algal blooms in recent summers, partly attributed to treated and untreated sewage.
(AFP)
