People advised not to enter the water for 28 days
It's thought foam used to tackle the fire within Castletown and Malew Fire and Ambulance Station may have resulted in the deaths of several fish in the nearby Silverburn River.
Officers with the Department of Environment, Food and Agriculture are investigating reports that the substance entered the watercourse during the incident.
A number of fish were found dead in the river near Poulsom Park this morning.
People are being advised not to swim in the river for the next 28 days.
DEFA is also advising pet owners to keep their animals away from a section of the Silverburn River between Ballasalla and Castletown harbour at this time.
Multi-agency response to fire in Douglas
General Election recount to take place at Douglas Courthouse
Planners approve further redevelopment work on Castle Mona
Airline schedule issues, rising fuel costs and cataracts on HoK agenda