Sulking Koi - why?

We have recently cleaned out our pond and pulled out some plants as the
pond was overrun with iris' and lillies. Before this our koi were
swimming about, feeding well and were almost tame, ie: approaching
surface and fedding well and sociable. Now however, they have "sunk" to
the back of the pond behind a clump of iris. They hardly feed and appear
to be sulking/hiding and ... basically doing absolutely nothing!

We are frantic with worry and thought we were making their pond home
nicer...!

What is wrong with them.... and more importantly will they recover?

Help.....!




--
Gedster