The eastern foot of Demavend is washed by the river Herhaz (called Lar river in its upper course), which there breaks through the Elburz in a S.-N.
It is situated on both banks of the Heraz, or Herhaz river, which is crossed here by a very narrow stone bridge of twelve arches and flows into the Caspian Sea 12 m.
Four rivers belonging essentially to Persia, in reference to the Caspian watershed, are the Seafid Rud or Kizil Uzain on the southwest, the Herhaz on the south and the Gurgan and Atrek at the south-eastern corner of that inland sea.
The Herhaz, though not important in length of course or drainage, also, like the Seafid Rud, breaks through the Elburz range from the inner southern scarp to the north.
The chief are the Sardab-rud, Chalus, Herhaz (Lar in its upper course), Babul, Tejen and Nika, and all are well stocked with trout, salmon (azad-mahi), perch (safid-mahi), carp (kupur), bream (subulu), sturgeon (sag-mahi) and other fish, which with rice form the staple food of the inhabitants; the sturgeon supplies the caviare for the Russian market.