More than 5,600 sewage dumps into Scottish waterways were recorded but not reported to the environmental regulator, figures show.
Scottish Water reported 14,008 sewage spills to the Scottish Environment Protection Agency (Sepa) as part of its 2022 report – a 30% increase on the previous year.
However, the Scottish Liberal Democrats say “big questions” must be answered after it was revealed an additional 5,668 spills were recorded in lochs and rivers in 2022.
The Scottish Water document which published the figures states the overflows were subject to monitoring through various licensing reporting requirements under the Water (Controlled Activities) Scotland regulations – but they had not been added to the annual Sepa publication.
It takes the total number of sewage dumps to 19,676 – 40% higher than previously thought, the Lib Dems said.
Party leader Alex Cole-Hamilton said that higher number is still likely to be an underestimate as many sewage overflows are not monitored.
He said the Scottish Government must “stop being the defenders of outdated sewage standards”.
Mr Cole-Hamilton said: “People will be disgusted to learn that sewage is being dumped into our rivers and waterways more than 50 times a day.
“Yet even this new figure is still likely to be a huge underestimate, as the vast majority of overflows are simply not monitored.
“Scotland is way behind England, where 91% of sewage outlets are monitored. Last year figures from just 4% of outlets in Scotland were reported to the environmental regulator Sepa.
“Both Scottish Water and Sepa have big questions to answer ahead of the publication of fresh statistics next month.
“It is time for the SNP to stop being the defenders of outdated sewage standards. They need to get tough with the Government-owned water company whose bosses pocket bumper bonuses while dumping sewage into our rivers.
“To turn the tide on this scandal, Scottish Liberal Democrats have published plans for a Clean Water Act that would see vital updates to our sewage network and clamp down on discharges.”
The party’s plans include modernising the sewage network and a requirement to monitor and publish every sewage dump.
There would also be a ban on dumping sewage in protected areas, including bathing waters.
Last week, figures obtained by the party using freedom of information legislation showed 2,099 complaints were made to Sepa about sewage in rivers, loch and seas between 2019 and 2022.
Scottish Water, Sepa and the Scottish Government have been asked for comment.