At the western end of a great bend in the river is the Belaga District, and further downstream are the Pelagus Rapids where the Iban people dominate.

Kapit is the last stop for express boats coming from Sibu, and is inhabited by the Chinese, Iban, and Kayan people.

[8][note 10] The biggest town on the banks of the river is Sibu, some 65 miles (105 km) upriver from the mouth of the Rajang.

[12][note 11] It can be reached by ocean-going vessels, and is the political, economic, cultural, and education centre of the central region of Sarawak.

Tanjung Manis District (16 miles (26 km) from the river's mouth)[12][note 14] is located near the Rajang delta where the Malay and Melanau people dominate.

[8][note 15] Bruit Island is situated inside the Rajang delta, with a lighthouse at Sirik Point.

Meanwhile, the Iban people migrated from West Kalimantan to the lower Rajang valley, moving their agricultural base.

Inter-ethnic conflicts followed the introduction of new tribes into the Rajang basin, and some ethnic groups fled to the Balingian and Tatau rivers.

[14] Subsequently, government offices, schools, a bank, a police station, a mosque, and churches were built around the fort.

The Ibans in the Rajang basin exchanged jungle produce with Chinese and Malay businessmen for salt, beads, metal, porcelain utensils, earthen jars, and coins.

Seeing the success of Chinese planting rubber trees and pepper vines, the Ibans also started to grow these cash crops.

Later, when the Chinese ventured into the logging industry, urban migration of the Ibans occurred, whilst the Kayans and Kenyahs grew rice, cash crops such as rubber, coffee, and groundnuts.

The Penans and Punans maintained a nomadic way of life, bringing jungle produce, woven items, and handicrafts for sale at local markets.

[15][16] Construction of the Bakun Dam on the upper Balui River, from 1997, resulted in the Sungai Asap resettlement scheme.

Totally protected mammals include gibbon, langurs, black giant squirrel, slow loris, and tarsier.

Other species of bird commonly found along the Rajang basin are the Pacific swallow, Little spiderhunter, and Asian glossy starling.

[19] the Empurau is still found breeding near the upper tributaries of Rajang such as the Balleh River, and also near the Bakun Dam.

[21] Other agricultural activities in the Rajang basin include the cultivation of rubber, pepper and vegetables, and poultry domestication.

[30] In September 2020, heavy rain in the upper tributaries of the Rajang caused flash floods in the low-lying areas of Kapit, Song, Kanowit and Sibu.

The log debris, stretching 50 km, reached Sibu on 8 October, causing transportation difficulties for the people living alongside the river and killed many fish.

[36] In August 2021, logjam blocked the Rejang River, shutting down the water treatment plants in Sibu.