One member of our house gifted a water dwelling plant from Santa Cruz's Antonelli Pond recently. He says "thank you for setting up the Yellow Flag Iris in the water feature: I'm sure the fish love it, especially little White-nose who is my favorite."
Don't be fooled by its humble appearance, the Yellow Flag Iris is actually illegal in several states due to its invasive nature. Since there is little risk of the plant "spreading downstream" in our little fish pond I see no reason why we shouldn't keep it, especially if it does well since its so hard to grow plants in that pond. Besides the fish really do need protection from the wildlife and Eleanor the cat.
Images taken from http://www.chicagobotanic.org/research/conservation/invasive/iris_pseudacorus.php
