Sanjiangkou is located in Tongjiang, Jiemusi City. It is where Songhua River and Heilong River merge in the northeast of Tonghong City. That is how it got its alias as Hongtong River. The Tongjiang government has developed the area where the sign on the Tongsan National Highway says 0th km into a tourist attraction site. The water of Heilong River is dark green, slow but wide, while the water of Songhua River is yellow-ish. After the two river merge, the water behinds significantly rapid, and the colors do not blend within ten miles.