Pollution of the Ballinderry River in Co Tyrone with effluent should be a thing of the past following the opening today of a £13 million wastewater treatment works in Cookstown.
Northern Ireland Water said the new works now brought the standard of wastewater discharge into the river into line with the latest European directives.
A clean-up of the river has resulted in fish spawning in waters they haven't been seen in for over 40 years.
The two-year project has resulted in a state-of-the-art treatment works facility capable of treating wastewater flow from a population of approximately 45,000.
NI Water's chairman and acting chief executive Chris Mellor said the Ballinderry River was a Special Area of Conservation and one of the most important rivers in Northern Ireland for rare aquatic species.
"The project team was not content with designing a new works that would simply comply with wastewater standards.
"They made it a priority to rectify some of the damage caused to the river through poor quality of effluent, which historically had been released to the watercourse from numerous sources," he said.
A year on from the works being commissioned, the transformation of the river habitat was remarkable, he said.
"Invertebrate species that only survive in very clean water can now be found in abundance and hundreds of fish are spawning downstream of the works.
"This significant investment will ensure that the facility will support growth and ongoing development in the Cookstown area, while contributing to environmental improvements," said Mr Mellor.
NI Water said it worked throughout the project with a number of key stakeholders including Alan Keys of the Ballinderry Fish Hatchery who said the new treatment works had completely changes the river environment for some five miles downstream of Cookstown.
"For example, we now have fish spawning at Killymoon and Ardtrea, which hasn't been seen in over 40 years. In addition, hundreds of big dollaghan (brown trout) are using the clean gravel to spawn and we now have great counts of young trout," said Mr Keys.