[7] The source of the Iwaki River is at Mount Ganmori (987 metres (3,238 ft))A in the Shirakami-Sanchi region, a mountainous, unspoiled expanse of virgin forest which spans both Akita and Aomori Prefectures.

[5] The river flows eastward as a small mountain stream,[6] then joins several tributaries to form the scenic Meya Ravine.

[1] It flows through the following municipalities: Nishimeya,[9] Hirosaki, Fujisaki, Itayanagi, Tsuruta, Tsugaru, Goshogawara, Nakadomari, and Shiura, where it enters Lake Jūsan.

[6] The Iwaki River region, located in the vast northern Mutsu Province, came under the control of the central government throughout much of the Heian period (794 – 1185).

By the mid-Kamakura period the Akita clan ruled the area, and the ranches, agriculture of the Iwaki River region, and trade with the Ainu.

[6] After the Meiji Restoration in 1868 the construction of railroads in Aomori Prefecture, specifically the Ōu Main Line, ended the comparatively inefficient riverboat trade along the Iwaki River in favor of the movement of agricultural cargo by rail.

In the 20th century the central government of Japan took direct control of riverworks to prevent flooding on the Iwaki, a chronic problem recorded as early as the Edo period.

The Iwaki River Improvement Plan (岩木川改修計画, Iwakigawa Kaishuu Keikaku) was officially approved by the Diet of Japan in 1917.

The mouth of the river at Lake Jūsan, Mitoguchi, suffered frequent blockage between November and April due to strong winds and waves, a feature of the harsh climate of northern Aomori Prefecture.

Numerous irrigation canals have been built across the Tsugaru Plain, and the Iwaki supports the paddies for vast production of rice in Aomori Prefecture.

[1] Aomori Prefecture is the largest producer of apples in Japan,[11] and the upper zone of the Iwaki River provides irrigation for an extensive network of orchards, especially in the area of Hirosaki City.

The yamato shijimi, a species of clam used in Japanese cuisine, is common in the brackish area of the mouth of the Iwaki River at Mitoguchi and Lake Jūsan.