In the middle of the village it is joined by the substantial tributary, the River Colwyn which drains the south-western flank of Snowdon.

This is a small rocky gorge close to the main road which provides easy public access to a most picturesque piece of Snowdonian scenery.

This wide flat valley – now called Traeth Mawr – was once the estuary of the Glaslyn before the Porthmadog Cob was created.

Once the river has crossed under the railway line, it meanders in large pools and marshes before eventually passing through the tidal sluices on the Cob at the south-eastern end of the town of Porthmadog, and from there into Tremadog Bay.

The first pair of breeding ospreys in Wales nest at Pont Croesor about 4 miles (6.4 km) upstream from Porthmadog where the RSPB have set up observation facilities.