DEFA is now continuing to monitor the area
Over 100 fish have been killed as a result of a pollution incident at Groudle Glen during TT.
DEFA and Manx Utilities have identified the source of the pollution as a surface water drain which serves a nearby housing estate.
Officials say 110 brown trout were found dead in a 200m stretch of water directly downstream from the pipe.
DEFA is continuing to monitor the area.
However, government says it's still not clear yet what exactly killed the fish despite samples being taken and tested.
People are being reminded to take extra care of what they dispose of down drains, sinks and toilets.
Anyone with concerns about what is going into surface water drains is asked to contact the Environmental Protection Team on 685 885.