1911 Encyclopædia Britannica, Volume 28… (1911)
“ In 1845–57 the outflow of the Nogat was stopped and an artificial channel was formed for it, so as to restore the proper head of water to the Vistula. Shifting banks form a serious impediment to navigation, and these and floods (principally in spring and midsummer) necessitate careful works of regulation. The river is ice-bound at Warsaw, on an average, from about the 20th of December to the 10th of March. The navigation of the Vistula is considerable up to Cracow, and the river forms a very important highway of commerce in Poland (q.v.) ”
