If your temps are high enough, water hyacinths will utilize a large amount of nutrients and can be kept quarantined with a floating border. I started with 8 plants last summer and pulled literally thousands of the floating plants out after the first freeze. I had several blooms but nothing came back this year so I know my winters are way too cold so I'm sure your winters would ensure that as well.
The situation Theo is referring to is a very cool wetland project I've read the history on and the key is having "X" volume of water in a semi-static state that allows plant to slowly remove the nutrient load but it's a continuous yet slow process that requires multiple parts. One to remove nutrients and another to trap unusable sediments. Very well thought out deal, wish I had the brains to build something similar.
