Eelgrass, tapegrass, or wild celery are all common names for Vallisneria. Eelgrass is a rooted submerged plant often found in flowing water. It has long, thin, ribbon-like leaves (1/2 - 3/4 inches wide) that are commonly 3 to 4 feet long. The vein pattern in the leaves of eelgrass is very distinctive and resembles celery. Eelgrass has a vast rhizome system that allows it to form dense colonies and usually excludes other submerged plants.
http://aquaplant.tamu.edu/database/submerged_plants/eelgrass.htm (http://aquaplant.tamu.edu/database/submerged_plants/eelgrass.htm)