Potamogeton crispus (Curly Pondweed) is submerged aquatic plant, widespread in the Old World, in Eurasia, Africa, and Australia, but it is clearly introduced to North America. The first definite records and herbarium specimens were collected from the Delaware River. Its spread was rapid: by 1900 it ranged south to James River, Viriginia and west. to Lake Erie; north to Lake Champlain and Montreal.. By 1930, it occurred in all the Great Lakes and the upper Mississippi Basin, and by 1960, in the Rocky Mountain States. There was a southward expansion in the 1930s-40s: reaching North Carolina in 1950; Florida in 1937; Louisiana in 1949, but the southern spread was slow and spotty .By the 1970s, P. crispus was also found through southern Canada. Potamogeton crispus was spread both by waterfowl and by deliberate planting as a wildlife food. It was probably introduced separately to California in about 1900, where it spread into the Sacramento-San Joaquin system in the 1940s-1950s. It occurs in fresh-mesohaline regions of major Atlantic estuaries from Chesapeake Bay to the St .Lawrence, including the Hudson River, and in the San Francisco Bay Delta, and the Columbia River estuary.