The Zijl branches off from the Old Rhine in Leiden, flowing in a northerly direction, where it intersects with the
Rijn-Schie canal (Rijn-Schiekanaal) that proceeds in a southerly direction. In the southern portion of its course, the river serves as the municipal boundary between Leiden and
Leiderdorp. In the southernmost section, both the west bank of Leiden and the east bank of Leiderdorp are densely urbanized. Moving north from the Driegatenbrug bridge, the east bank gradually merges into the open grassland of the
Boterhuispolder, which remains under Leiderdorp's jurisdiction in this area. Beyond the Leidse
Merenwijk, the Zijl enters entirely into the territory of
Warmond (municipality of
Teylingen). Along its eastern bank in this stretch runs the Zijldijk, a road that leads to a dead end for traffic. On the western side of the Zijl, beyond Leiden, within Warmond's jurisdiction, lies the remnant of the
Broek and Simontjespolder, followed by the island of De Strengen with its long northern spur, Tengnagel (which is only a few tens of meters wide). Adjacent to the western side of Tengnagel is 't Joppe, one of the most frequented navigated areas within the Kagerplassen. North of the tip of Tengnagel, the Zijl remains in direct connection with 't Joppe. A few hundred meters further north, at the northernmost point of the
Boterhuispolder and the
Kaagsociëteit, the Zijl converges with the Kager Lake Zweiland, along with the
Zijp (which flows in from the southeast). During the summer, a
ferry operates over the Zijl, providing service from the Zijldijk to the Broek and Simontjespolder in the Kagerzoom, situated just above the Leiden Lakes District. == History ==