Polska Żegluga Morska known as Polsteam or PŻM, is a cargo ship operator based in Szczecin, Poland.

A Chinese-built ship owned by the company, MS Polesie, caused the crash into and sinking of British-flagged MS Verity on 24 October 2023 in the North Sea[1] Polsteam was founded in 1951, nationalizing the assets of two Polish pre-WWII marine freight companies (Gdynia America Line and Żegluga Polska [pl]), making it the oldest Polish cargo ship operator in existence.

[4] Polsteam also operates a passenger ferry service between Świnoujście and the Swedish ports of Ystad and Trelleborg via its subsidiary Unity Line.

The PZM line operates a bi-weekly service from the IJmuiden docks in Amsterdam to the North American port of Duluth, Minnesota.

[5] The dimensions are limited by the locks of the Saint Lawrence Seaway and the 40 ft draught of the Great Lakes Waterway.