Approximately 400 litres of a chemical coagulant were discharged into the River Eden in Fife in October 2018.
On Monday Dundee Sheriff Court heard on October 2 that year, a forklift truck operator punctured a large chemical container with the forks of the vehicle while attempting to move it from storage at the Cupar Waste Water Treatment Works.
Around 500 litres leaked out onto the forecourt of the works before the operator managed to turn the container over in an attempt to prevent further spill and moved it to another corner of the site.
However, the chemical leaked from the spill site to the rear of the works and entered the river in several locations.
There was also an attempt to clean up the chemical spill by hosing and mopping it into nearby surface water drains – which flow into the River Eden.
Later that day members of the public reported dead fish in the river to the Scottish Environment Protection Agency (Sepa).
During an investigation Sepa found there was a lack of knowledge among Scottish Water employees regarding the harmful effects of the chemical and the importance of preventing it from entering the water environment.
‘We take our environmental responsibilities seriously’
Site staff were found to not be appropriately trained in emergency spill response and were unaware the surface water drains on site discharged into the river.
Most of the fish killed were brown trout but there were also salmon and sea trout, and the incident is likely to impact their numbers in the area for four or five years.
Scottish Water pled guilty to a charge under section 20(3)(a) of the Water Environment and Water Services (Scotland) Act 2003.
A company spokeswoman said: “We take our environmental responsibilities very seriously and since the incident have taken action to reduce the risk of a recurrence at the Waste Water Treatment Works.
“This includes changing the way the substance involved – a chemical used in the treatment process – is stored and handled.
“We have also made improvements to drainage on-site and provided improved training for staff.”