Cleaning the Water Lily Pond

Drained pond at Wenying Park in Taiyuan

I saw the two men in the above photo working together to spray water underneath the large leaves of water lilies in the drained pond. The man with the hose also sprayed water at areas of the pond's bottom not covered by water lilies. I believe the genus of these large water lilies is Victoria but am not sure of the species. I can't find any information about caring for them that recommends draining a pond, expect for transplanting. The previous time I passed the pond, it was filled with water and contained similar, if not the same, floating water lilies. While it appears to be a cleaning of some sort, I am not sure what may have motivated it. I would welcome any insights from water lily or pond aficionados.

Most of today I was focused on non-lily matters. I welcomed the momentary diversion the water lilies provided both at the park and more recently while I learned a bit more about how to care for them.