An estuary on the east coast of Scotland at the mouth of the River Tay, the Firth of Tay extends eastwards from the confluence of the Rivers Earn and Tay, opening into the North Sea beyond Buddon Ness in Angus and Tentsmuir Point in Fife. Its channel is 23 miles (37 km) in length and although quite narrow, because of sandbanks, has a maximum width of 3 miles (5 km) at Invergowrie to the west of Dundee. The Firth of Tay is crossed by the Tay Road Bridge and Tay Railway Bridge at Dundee which is the principal port and settlement on the estuary.
The upper estuary has extensive reed beds, planted in the 18th century to prevent the erosion of the river banks and now the largest in the UK, with an area of more than 800 ha (1977 acres) or 15% of the total reed in the Britain. With much marshland having been drained for agriculture, this now represents a scarce and important habitat. Traditionally harvested for thatching, this industry was revived in the 1970s and continued until 2005, when it became uneconomic due to competition from Eastern Europe.
It was from the Firth of Tay that a record-breaking flight began on 6th October, 1938. A sea-plane was launched via the Mercury-Maia piggy-back combination and reached South Africa having flown for 6045 miles (9728 km) without refuelling, which remains a record for sea-planes. The flight is commemorated by a plaque overlooking the estuary at Dundee.