The area around Hwachiang Bridge, explains Fang Wei-hung, a member of the Wild Bird Society, is suitable for the ducks because the river there is broad and slow and has formed numerous bars from the mud and silt brought down from upstream. As the tide retreats, the ducks like to stick their bills into the mud and sand and seek for algae, shells, insects, or other kinds of food.
台北市野鳥學會的方偉宏認為，華江橋一帶正處在新店溪與大漢溪的交會口，河道寬，水流緩，溪水從上流所夾帶的泥沙在此淤積，形成肥厚的沙洲，由於受到淡水河出海口潮汐的影響，退潮時，水鴨喜歡用扁扁的嘴，貼在泥沼上搜食留下來的浮游性藻類、貝類或小蟲。