The River Ogwen (Welsh: Afon Ogwen) is a river in north Wales draining from some of the greatest peaks in Snowdonia before discharging to the sea on the eastern side of Bangor.

The source of the Ogwen is in Llyn Ogwen, which can be seen alongside the A5 road as it starts to descend through Snowdonia. However, the true source of the river lies in the three streams draining into Llyn Ogwen. These are Nant Gwern y Gof, Afon Denau, and Afon Lloer which itself has its source in the upland lake, Ffynnon Lloer.

The River Ogwen emerging at the western end of Llyn Ogwen immediately descends cataracts and waterfalls know as Ogwen falls before continuing in a north, north westerly direction down the glaciated Nant Ffrancon valley.

In the 1950s and 1960s, this stretch of the river was re-engineered to try to help drain the adjoining farmland. However, the beneficial effects were not significant and the ecological damage was great. In the 1990s, the Environment Agency, working with partners including the Countryside Council for Wales and farming groups, re-engineered the river to recreate pools and riffles with the intention of allowing the river to re-gain its original form and diversity of wildlife.

As the river continues northwards, it passes close to the great waste tips of slate produced by the Penrhyn slate quarry and then past a caravan site where the remains of a long abandoned mill and mill pond still exist. Passing Braichmelyn village on its eastern bank, it is joined by the substantial tributary, the Afon Caseg, which drains a large area of the Carneddau mountains. The course turns slightly more westwards as the river passes through Bethesda and becomes progressively more wooded and more deeply cut providing some white water conditions enjoyed by canoeists.

The widening river then follows an abandoned railway line (now a pleasant cycle path) through a wooded valley crossing under the main north Wales coast line and the A55 before discharging to the Menai Straits at Aberogwen near Bangor.