The river drains 557,180 km2 (215,130 sq mi) of land, and has an annual discharge of 76.2 km3/a (2,410 m3/s) to 81.77 km3/a (2,591 m3/s).[4][1][3]
The extreme flatness of theNortheast China Plain has caused the river tomeander over time, filling the wide plain withoxbow lakes, as remnants of the previous paths of the river.
From there it flows north, to be interrupted by theBaishan,Hongshi andFengmanhydroelectric dams. The Fengman Dam forms a lake that stretches for 62 kilometers (39 mi). Below the dam, the Second Songhua flows north throughJilin, then northwest until it is joined by its largest tributary, theNen River, nearDa'an, to create the Songhua proper.
The Songhua turns east throughHarbin, and after the city, it is joined from the south by theAshi River, and then by theHulan River from the north.
A new dam was constructed in 2007 nearBayan (50 km northeast ofHarbin), creating the Dadingshan Reservoir,[5] which is named after the scenic area on the south bank (Chinese:大頂山;pinyin:dàdǐngshān;lit. 'Big Topped Mountain').
The river freezes from late November until March. It has its highest flows when the mountain snow melts during the spring thaw. The river isnavigable up to Harbin by medium-sized ships. Smaller craft can navigate the Songhua up toJilin and the Nen River up toQiqihar.
In November 2005, the river wascontaminated with benzene, leading to a shutdown of Harbin's water supply.[citation needed] The spill stretched 80 kilometers (50 mi) and eventually reached the Amur (Heilong) River on theChina–Russia border.[6] On July 28, 2010, several thousand barrels from two chemical plants in China's Jilin City were washed away byfloods. Some of them contained 170 kilograms (370 lb) of explosive material liketrimethylsilyl chloride andhexamethyldisiloxane.[7][8] In 2016, the part near the city of Jilin was affected by a minor flood.
