Newcastle airport is in the catchment of the Ouseburn, a tributary of the Tyne. Deicing chemicals have affected the river for many years and the company has fitted a monitoring system to divert polluted run-off from runways and a hard standing area to sewer.
Urea-based deicers were used at the airport until the early 1990s, when they were phased out because of their impact on water quality. Propylene glycol is now used instead - although it has a high biochemical oxygen demand.
The company's monitoring system measures the BOD of run-off held in a lagoon and diverts water containing more than 10mg/l of BOD to sewer. Its consent to discharge to a tributary of the Ouseburn specifies a limit of 15mg/l.
The incident happened last January, when the company notified the Environment Agency after a fault in the system had allowed polluted drainage into the stream.
Newcastle International Airport was charged with causing polluting matter to enter controlled waters, contrary to section 85(1) of the Water Resources Act 1991.
The company pleaded guilty before Gosforth magistrates on 13 January, when the court heard that Agency monitoring showed that BOD in the stream had reached 1,280mg/l - 85 times the limit in the airport's discharge consent.
No fish were killed, but pollution control staff said that there had been no fish in the stream for many years because it is so polluted. Following the incident, downstream water quality was so poor that only the most pollution-tolerant species would be expected to survive.
The discharge occurred just a few months after the airport accepted a formal caution from the Agency over a similar incident involving propylene glycol in winter 2002.
In mitigation, the company said that it regretted the incident but had invested in the latest technology to try to prevent pollution. It had also employed environmental consultants to examine drainage issues at the airport.
Newcastle International Airport was fined £10,000 and ordered to pay costs of £901.
Agency special enforcement team leader Andy Rothery commented: "This is the latest in a series of pollution incidents at Newcastle airport and the fine rightly reflects the seriousness of these incidents. Repeated pollution of the burn is preventing the ecology from recovering, which I'm sure locals would like to see."