iI have a well-stocked fish pond and is very healthy and clear. But in the winter some of my fish die through Leeches which suck them and make them weak and they die. Is there anything I can do
The simplest method to reduce leech numbers would be to make some traps.
To do it properly would involve draining the pond, removing the fish and plants, just for starters!
Leeches are nasty parasites, the world can do without. (i m o)
In the first instance I would look for a solution that will not affect other harmless pond life.