Large gulf of the Baltic Sea .
Bounded by Latvia and Estonia, it covers about 7,000 sq mi (18,000 sq km). The gulf, icebound from December to April, has a maximum depth of 177 ft (54 m). The coasts are mostly low and sandy, and several important rivers, including the Western Dvina , reach the sea there. Several ports and resorts, including Riga , line its shores.