The chemical attacks the fish's central nervous system so we're going to have an ongoing mortality rate over the next few days

Hatchery manager Richard Turner

Hatchery manager Richard Turner said he did not know why the organisation had been targeted.

"I cannot understand why anyone would lower themselves to carry out this act," he told BBC Radio Ulster.

"Potentially we are looking at five years work which could be wiped out. People are just devastated.

"With this sort of chemical there'll be an initial kill.

"But it appears it attacks the fish's central nervous system so we're going to have an ongoing mortality rate over the next few days."

Mr Turner said the business had widespread community, cross-border and local government support.

He said the chemical could also affect fish further downstream, near the river mouth.

Mr Turner said it would take up to five years to replace the stock.

Meanwhile, detectives investigating the incident are keen to hear from anyone who saw any suspicious acivity in the area of the Marble Arch Road late on Saturday night or early on Sunday morning.