The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from 10°E to 30°E longitude. It is a shelf sea and marginal sea of the Atlantic with limited water exchange between the two, making it an inland sea. The Baltic Sea drains through the Danish straits into the Kattegat by way of the Øresund, Great Belt and Little Belt.
https://en.wikipedia.org/wiki/Baltic_Sea