Potamogeton pusillus is a species of aquatic plant known by the common names small pondweed, lesser pondweed or least pondweed. It occurs in standing and slow-flowing freshwater habitats throughout the Northern Hemisphere. Lesser pondweed is widely distributed globally, occurring across most of Europe (including Scandinavia) and North America. It is reported from scattered locations in Central and Southeast Asia and is widespread in China. It is also widespread in South America and Africa. Ecology and Lesser pondweed grows in standing or slow-flowing water bodies such as ponds, lakes, ditches, slow-moving streams, and river backwaters. It is a lowland plant and requires calcareous water, with a marked preference for high nutrient levels, and may form extensive beds in favourable situations, growing with other nutrient-tolerant species such as Myriophyllum spicatum and Zannichellia palustris. It is tolerant of turbid water and is a good colonist, often exploiting temporary or disturbed habitats such as livestock drinking ponds, canals and ditches. In lakes it is very tolerant of eutrophication and the resulting competition from phytoplankton and periphyton, and is often one of the last submerged plants to disappear.