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How did the Brahmaputra River become known as the Jamuna River in Bangladesh?

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Map showing the course of the Brahmaputra River as it flows from southwestern China through northeastern India and into Bangladesh, with surrounding countries including Bhutan, Nepal, Myanmar, Pakistan, and Afghanistan labeled. The river's path is highlighted in blue, and major international boundaries are marked. — Brahmaputra River Brahmaputra River.

The Brahmaputra River became known as the Jamuna in Bangladesh due to a significant hydrological shift that occurred in the late 18th century.

Until the late 1700s, the main course of the Brahmaputra flowed past the town of Mymensingh to join the Meghna River. However, in 1787, an exceptionally high flood caused the Tista River to divert its waters eastward into an old, abandoned channel known as the Konai-Jenai.12

This influx of water from the Tista reinforced the Konai-Jenai, which had previously been a minor spill channel. The Brahmaputra began to cut into this new path, and by 1810, it had been transformed into the river's main lower course, which is now called the Jamuna. The original path of the river, which still flows past Mymensingh, is now known as the Old Brahmaputra.123