Sorry, I hit send by mistake.
(I also take out the water hyacinth--)
After the 1st freeze, I use a "Thermo-Pond" 100 watt heater and a air
pump with a spliter that goes to (2) four inch disc bubblers. The pond
freezes at times to about a 4 or 5 inch depth, but the heater combined
with the bubbler, keeps a hole open all winter. I usually disconnect the
waterfalls in late Dec. or early Jan. unless it is a really cold winter.
I haven't lost a hardy lily yet.