How and when did the Yellow River turn yellow?

Through on-the-spot investigation, the Yellow River flows from the source of Yuegu Zongle Canal to Zhaling Lake and Eling Lake. Most rivers flow through mountainous areas with bare bedrock, and the sediment content in the water is very small, which becomes clearer after being injected into Zhaling Lake and Eling Lake for precipitation. Therefore, the Yellow River water discharged from Yeling Lake is still clear and transparent. However, when it flows from Erling Lake to "Dazhaling Lake Township" section 15-20km, the water begins to be turbid and yellow. The reason is that there are a large area of Quaternary loose sediments in Dazhaling Lake Township, all of which are yellow mud and sandy soil, which are easily swept away by the current. There are many tributaries of the Yellow River in this area. Due to the changeable climate, it rains and snows, and flash floods occur. Scholars have measured that the sediment transport rate of the Yellow River here is 803 kilograms per second. Therefore, it is determined that the Yellow River water began to turn yellow from Dazhaling Lake Township.