The River Cong is a river in Ireland. Rising in the village of Cong, County Mayo. It is the outflow from Lough Mask, further to the north, that escapes through huge fissures in the cavernous limestone of the district and rises again in the village of Cong. It is about one mile long. The river is some 100 yards wide in places, and divided by an island at one point. It pushes down strongly past Ashford Castle. The River Cong has a mean flow rate of 37.6 m³/s