I know a proverb:

It's called Jiang, and there is plenty of water all year round, which always gives people the convenience of boating.

Generally, the dry season becomes a trickle, and the river is the one without boats to weave.

Songhua River conforms to this statement.

There is another saying:

In China, rivers that flow into inland seas or lakes are usually called rivers. For example, the Yellow River flows into the Bohai Sea and is called a river; Liaohe River, which flows into Bohai Sea, is called River; Tarim River flows into Lop Nur, also known as the Great River, and so on. Rivers that flow into the high seas or oceans are usually called rivers. For example, the Yangtze River flows into the Yellow Sea, which is called Jiang; The Pearl River that flows in is called Jiang, and so on. We can also look at other rivers: Heilongjiang, Pearl River, Wusuli River, Nujiang River, salween, Qiantang River and Yarlung Zangbo River.

Of course, the names of rivers in Chinese mainland all have this feature, and it is customary that rivers on our island, no matter where they are injected, are called rivers or streams, such as Wanquan River, Turbid Water Stream, Dajiaxi and so on.

For foreign rivers, no matter how long they are, whether they are injected into inland seas, lakes or open seas or oceans, they are generally called rivers. For example: Nile, Amazon, Mississippi, Lena, Yenisei, ob river, San Lao Lun, La Plata, ... Even if it flows into the ocean, it is still called a river. There are few rivers called Jiang abroad. Even if there is, it is related to China, such as Heilongjiang, Tumen, Wusuli and Nujiang ... The only foreign river is called Jiang, because for a long time, it was a vassal state of China, paying tribute to China and having close ties with China.

The Songhua River, a tributary of Heilongjiang, flows into the open sea, which is also consistent with this statement.