anacharis substitute? (it's illegal in Maine)

Hi there,
I have two new half-barrel ponds. I put a water lily and two marginals
in each of them. I'd like to get some more plants, particularly something
that can provide oxygen and prevent algae. In my research, I've heard
glowing reviews of anacharis for this purpose. However, I just learned that
anacharis is illegal in the state of Maine so I can't buy it anywhere.
(It's also illegal to put goldfish into any outdoor pond, even a barrel!)
I'm wondering if anyone has other suggestions for floating or submerged
plants that can help me round out my ecosystem. Does anyone else keep ponds
in Maine, or are the laws too restrictive? It's a real shame, given that
there are so many natural bogs and other wetlands, that we are so restricted
in terms of recreating one in our own yards. I growing discouraged about
the possibility of putting a more ambitious water feature in my yard with
all of these regulations.

Thanks for any tips.
Brian