New Invasive Plant in Millstone River?

 A friend sent me a couple photos of a plant she says has spread rapidly in the upper Millstone River (upstream of the bridge at Route 1 and Harrison Street). My guess from the photos would be sweetflag, but there's no evidence of the characteristic spadix (a fruiting body that sticks out the side of the vertical leaf).

The plant's expansion is making it hard to negotiate some parts of the stream. The plant's identity awaits the retrieval of a specimen.

Whether it's sweetflag or not, some interesting info about sweetflag, its history, uses, and association with American Indian settlements can be found here.