Answer
Zhengde's fatal accident took place on the turbulent waters of the Yellow River, a natural calamity that tragically ended his reign. Zhengde's expedition against the Mongols brought him to the banks of this mighty river, where his boat capsized in the treacherous currents. The unpredictable and unforgiving nature of the Yellow River proved too formidable, resulting in the untimely demise of the Ming emperor.