Please explain 'there is no draining this pond'
Can't be done?
legal issues?
No access to equipment to drain?
No power?
GSF may stay dominant forever despite LMB. Is that a problem?
If you can't drain the water or choose not to, you may want to engage a thorough fish kill, that way you don't have to drain but still will have a fighting chance of changing the balance of fish in the pond.