The Blackwater or Munster Blackwater (Irish: An Uisce Dubh, The Black Water) is a river which flows through counties Kerry, Cork, and Waterford in Ireland. It rises in the Mullaghareirk Mountains in County Kerry and then flows in an easterly direction through County Cork, through Mallow and Fermoy. It then enters County Waterford where it flows through Lismore, before abruptly turning south at Cappoquin, and finally draining into the Celtic Sea at Youghal Harbour. In total, the Blackwater is 169 kilometres long.
The Blackwater is notable for being one of the best salmon fishing rivers in the country. Like many Irish and British rivers, salmon stocks declined in recent years, but the Irish Government banned commercial netting of salmon off the coast of Ireland in November 2006.