At Bonn the river enters the plains, and almost immediately after
passing the Netherlands frontier its delta begins. The principal arm,
carrying two-thirds of the volume, flows under the name of the Waal, and
later the Mermede, to Dordrecht, picking up the Maas (Meuse) from the
left. At Dordrecht the river again divides for a bit, one branch, the
old Maas, running out to sea; the other, the Noord, forming a loop by
way of Rotterdam. The northern arm sends one branch, the Yssel, due
north to the Zuider Zee; the other branch is the Lek, which runs into
the Waal-Maas arm above Rotterdam.
A thin stream, called the “Winding Rhine,” leaves the Lek and splits at
Utrecht into two channels, of which the Old Rhine, a mere ditch, manages
with the help of a canal and locks to struggle into the North Sea at
Katwyk, northwest of Leyden, while the Vecht flows due north from
Utrecht to the Zuider Zee near Amsterdam. In the delta the streams have
to be bordered by dykes.