It is a marginal plant, grown at a depth of about 15cm. Commonly known as buttercup. It is said to be a good filtration plant but I don't know if that means it is a good oxygenator though. Oxygen weed would be much better and is free.
I haul it up in bunches, with roots intact, from local rivers and plant it into baskets. If I am only using it over summer for spawning in a spare pond I just hold it down with a rock or brick.
Choose your collection spot carefully. Look for excess algae or unwanted critters. Water with a good flow is best.
A clear pic of the legal species can be found on our plant database http://www.fnzas.org.nz/?p=956