If left unmanaged, lily pads can spread rapidly and limit use of your pond.  They reproduce by horizontal tubers that run through pond mud, usually in water less than three feet deep. They also sprout from seeds that you see in the beautiful pod after a bloom.  Lotus can be managed with approved herbicides.  Treat leaves as they appear on the surface.  Leaves have a thick, waxy coat that must be penetrated for effective results.  Check with your state regulatory agency and a certified, licensed applicator for approved herbicides.