This huge basin holds and delivers the water supply to Belfast. It was created in the 1920's in response to the rapidly growing demand for water in the city. Several sites were considered for the project, and the Mourne Mountains were chosen because of the purity of the local water supply and the generous rainfall that is common to the area.
The Mourne Wall catchment portion of the reservoir took about 18 years to build. It was constructed by hand and took thousands of men to complete - nine of them died in the process.
The Binnian Tunnel was completed in 1951. It is 2 ½ miles long and travels deep below Slieve Binnian. The tunnel carries water from the Annalong Valley into the Silent Valley Dam. The eight foot tall tunnel was built using only candlelight by 150 men, and empties into a dam near the Visitor's Centre.