The Gulf of Bothnia is an arm of what sea?

The Gulf of Bothnia is the northernmost arm of the Baltic Sea. It is situated between Finland's west coast and Sweden's east coast. In the south of the gulf lie the Åland Islands, between the Sea of Åland and the Archipelago Sea.

The gulf is 725 km (450 mi) long, 80–240 km (50-150 mi) wide and has an average depth of 60 m (200 ft, 33 fathoms). The maximum depth is 295 m (965 ft, 161 fathoms). The surface area is 117,000 km² (45,200 sq mi). The northernmost point is situated in Töre in the Bothnian Bay. its coordinates are 65° 54'07" N 22° 39'00 E.

The depth and surface area of the Gulf of Bothnia are constantly decreasing, as the land is rising after it had been pressed down by the continental ice during last ice age. The rise is 80 cm every hundred years.