This floating water plant while invasive and not to be released in the natural environment, is the best friend of small pond owners who's water quality lacks from adequate filtration.
They make good breeding mats for Koi eggs (if your Koi leave them alone that is) and they can be placed in the pond when the fish begin spawning and some eggs will cling to them allow you to easily remove the plants and have the babies hatch elsewhere. They generally bloom in summer or fall.