The most important of these waterways is of course river IJssel; others include the Zwarte Water and (Overijsselse) Vecht rivers; the Regge stream, which flows through Twente to spend its last few kilometers in Salland before ending in the Vecht near Ommen; the Schipbeek stream; and the Soestwetering stream, which merges with a number of lesser streams near Zwolle to form river Zwarte Water.
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The region is most likely named after the river IJssel, anciently known as Isala, and the lakeland Sallzee at the confluence of the rivers Vecht and IJssel.