I think you have water primrose.
http://www.fosc.org/WaterPrimrose.htmThe grass carp if effective will need to grow or be larger to consume the more fibrous water primrose. In the meantime you may be able to chemically control it with some spot sprayings of
Chemical Control Options
The active ingredients that have been successful in treating water primrose include 2,4-D (E), diquat (E), triclopyr (E), glyphosate (E), imazamox (E), and imazapyr (E). E = excellent, G = good
This site says
http://aquaplant.tamu.edu/management-options/water-primrose/Biological Control Options
There is no known biological control for water primrose, although goats are known to forage on many types of emergent vegetation.