High, runs north-west past Czcnstochowa, separating the Oder from the Warta (Warthe).
- Russian Poland belongs mostly, though not entirely, to the basin of the Vistula - its western parts extending into the upper basin of the Warta, a tributary of the Oder, and its north-east spur (Suwalki) penetrating into the basin of the Memel, of which it occupies the left bank.
The Warta (450 m.) rises in the Czenstochowa hills, 900 ft.
Another canal, to the west of Leczyca, connects the Bzura, a tributary of the Vistula, with the Ner and the Warta; and the bed of the former has been altered so as to obtain regular irrigation of the meadows along its banks.
Another group of small lakes is situated in the basin of the Warta (north part of Kalisz), the largest being Goplo, 18 m.