People are being urged not to pour chemicals down domestic sinks or drains after 110 fish were found dead in a river in the east of the Isle of Man.
The brown trout were discovered in Groudle Glen during the TT festival.
While the source of the issue is not known, it is believed to be a chemical rather than sewage-based pollutant.
Environmental protection officer Danielle Coombes said the origin had been narrowed down to an area of residential housing nearby.
Ms Coombes said officers had "educated those residents on what to look out for" and "what to report if they have any concerns".
Water samples collected from the river did not return "any definitive results" and officers were continuing to monitor the area, she added.
Teams from the Department of Environment, Food and Agriculture and Manx Utilities (MU) were called out the incident.
Head of sewerage at MU Tim Woakes said small quantities of domestic cleaning products, which were highly diluted with water, "won't cause an issue".
However, larger volumes of substances such as bleach used for cleaning items including outdoor hot tubs would be harmful, he continued.
"We just need people to be responsible really and think about what they're doing before they take action," he added.
Mr Woakes explained that MU teams cleared about 200 blockages from the sewer network each year, the majority of which were caused by "the misuse of people's toilets and sinks".
"The main culprits are wet wipes down the toilets and oil and fats in kitchen sinks," he said.
"Each of these blockages not only costs a significant amount of money to clear, but it also hugely increases the risk of sewage spilling into streams and rivers and damaging our environment."
Why not follow BBC Isle of Man on Facebook and Twitter? You can also send story ideas to IsleofMan@bbc.co.uk
Isle of Man Government - Environmental Protection Unit
Fossil fuel boiler installations in new builds 'frustrating', says minister
Airlines 'need to do more to keep Island connected'
Lack of public disabled changing places with ceiling hoist 'not good enough' says MHK
MWT offering free small shark tagging training
Manx Museum launch Cabinet of Queeriosity
Learn Manx and beach clean along the way
US abortion clinics begin closing after landmark ruling
Man charged with terrorism after Norway shooting
UK PM: I will not undergo psychological transformation
Driving through Russia to escape war in Ukraine
Why this is a seismic day in America
Elation and despair outside US Supreme Court
What is Roe v Wade ruling on abortion?
Rifts split America's abortion 'ground zero' state
The moment Roe v Wade was overturned. Video The moment Roe v Wade was overturned
The Japanese street snack that took over the world
Fury and questions over China's treatment of women
'They'd rather die than return to Nicaragua'
Why top chefs are leaving Paris
"It started before Covid, but it was discreet"
The films bringing sex work to life
Has cinema perpetuated damaging stereotypes?
A growing and influential intellectual movement aims to understand why human progress happens – and how to speed it up
© 2022 BBC. The BBC is not responsible for the content of external sites. Read about our approach to external linking.