From scum on ponds to water celery on river beds and reeds swaying in a wetland breeze, freshwater algae and plants provide oxygen to breathe and food to eat.

• 从池塘的浮渣到河床上的水芹，以及沼泽微风中摇摆的芦苇，淡水藻类和植物提供呼吸之用的氧气和食用的食物。