There are hardy hybrid water lily varieties that are less aggressive. RAH the variety that you have mush be a bigger Medium or Larger spread variety. There are small Medium, Small, and Dwarf varieties. If one wants only a few slow spreading lilies choose colors in the small or dwarf variety. New lily owners -do your homework before adding water lilies if size and depth of the spread is a goal.

RAH - you can control or trim your beds of lilies by selectively spraying the pads with blend - mixtures of glyphosate with surfactant / sticker. Your lilies are not real fast spreaders. If you want faster spreading water lilies plant wild native white water lilies. Then you will see 'fast' spreading water lilies. To some extent soft mud bottoms and clear water allow water lilies to spread into deeper water.