Tremadog Bay is a large inlet of Cardigan Bay, defined by the north Cambrian Coast and the Llŷn peninsula of north Wales.
The River Glaslyn flows into the north of bay and St Tudwal's Islands lie at the western end of the bay. Pwllheli -the main market town of the Llŷn Peninsula- along with the historic towns Harlech and Cricieth, and Abersoch -a popular location for water sports- all lie on its shores.