We have a one acre pond and its wild... we have seen it through years of draught and flood. At one time it was covered with lotus leaves and although at first we thought that they were wonderful we came to realize that they were one giant soul sucking organism. Mr. Mercat got a small kayak and some eco friendly plant killer and slowly got rid of most of it. We leave a few. They do help keep the pond clean. We have a lot of turtles. The snappers thankfully are rare and they migrate. The muskrats were driven off by used cat litter in their holes. We had some really nasty long algae while the pond was dealing with the dead lotus leaves but it has cleared out. So if 3 koi aren’t keeping things happy, get rid of them and try some other fish that loves to eat algae. Grass carp might work.
So did you dig it there or was it there to begin with? What would happen if you or no one else cleaned it up? Wouldn't mother nature in its own way take care of the lotus leaves?