Finland, Gulf of
Gulf of Finland, eastern arm of the Baltic Sea, c.285 mi (460 km) long and from c.10 to c.75 mi (15–120 km) wide, between Finland and Russia and Estonia. The shallow gulf receives the Narva River and water from Lake Lagoda and the Saimaa lakes; it is frozen from December to March. The gulf, an important corridor for Russian and Estonian shipping, contains many islands. St. Petersburg and Tallinn (Estonia) and Helsinki (Finland) are the chief ports.