Dig up and transplant most water plants as soon as you can recognize what they are by new growth. Midsummer transplant is also usually okay. In fall some of the underwater forms are collapsing and hard to recognize. Many of the marginals and lilies can be moved in fall.

For water plantain dig and move it early in the season. You can move bulrush any time you can recognize it by stem or root. Bulrush is tough to kill and you don't have to be too careful in the transplanting process. Just get a good sized root mass and plant at a similar depth as it was removed from. After bulrush gets established watch it closely when it starts spreading it can move pretty fast. For control use rubber gloves with a brown cotton gloves on top of rubber gloves, wipe the perimeter stems with Round-Up. Water plantain will probably never be an invasive problem for you.

aka Pond Doctor & Dr. Perca Read Pond Boss Magazine -
America's Journal of Pond Management