Occurs in the pre-reform spelling Russian: Старой Iюсъ, romanized: Staryy Iyus, lit.

In the annual course of the water regime, spring floods are distinguished (starting from the second or third decade of April, lasting up to a month), summer-autumn (lasting 2–4 months) and winter (from late October to early November) base flow.

The average annual water consumption is 43.1 m3/s (1,520 cu ft/s) according to Stream gauging station in Sarala about 55 км from Source of the Cherny Iyus river.

The waters of the rivers of mountainous regions, in the nutrition of which high-mountain snows and glaciers[8][9] play a significant role, are characterized by a bicarbonate-calcium composition and very low (less than 0.1 g/dm³) mineralization.

[11] After the confluence of the rivers Big and Small Inzhul, Kolchakovsky stream, the general direction the river flow changes sharply to submeridional, the width of the valley increases to 3 km (1.9 mi)-5 km (3.1 mi) (near the village of Chebaki and the village of Gaidarovsk).

[11] On this section of the valley, they flow into the Black Iyus River: on the left – small rivers and streams Systygchul, Stuchul, Blinzhul, Kerebezhik, Tranzhul, Sektinsky, Pelageikin, Chesnokov; on the right – Belaya Pilnya, Martachul, Izekiyula.

After the confluence of the river Sarala Black Iyus again changes its direction to sublatitudinal, the width of the valley increases to 1.5 km (0.93 mi) – 2 km (1.2 mi), it also has many ducts, branches, small lakes and oxbow lakes, the longitudinal slope decreases to 0.0015.

[17] The earliest scientific and cartographically accurate description of Cherny Iyus river region was done by German doctor and naturalist Daniel Gottlieb Messerschmidt in the expedition on the territory of the Yenisei Siberia 1720–1727[18] who was personally accepted into the Russian service by Peter the Great.

In it was described by German historian and geographer Müller Gerhard Friedrich in his notes during Great Northern Expedition 1733 -1743,[19] at that time upper part of Chulym also was called Iyus.

[25] in 1967, a teacher at the Novokuznetsk Pedagogical Institute, Pyotr Stepanovich Shpin discovered the first glacier in the upper reaches of the Black Ius River with an area of 0.2 km2 (0.077 sq mi), the results of the following expeditions of 1968–1975 a Catalog of glaciers was compiled, aerial photographs were analyzed and a whole glacial system was discovered, consisting of cirque, hanging and slope glaciers with a predominantly northeastern exposure.