A native plant (despite its common name). Apologies for delay in responding, just picked this up recently. In most cases, dislodging of vVallisneria is caused by one or more of the following: wave action (from wind, power boats), fish (carp, mumbling).
Unfortunately whiteish/brownish shades are common to several genera and, without any view or information about the stem and gills, it's hard to suggest an ID.
