Heron Visited my Pond

Hi, my pond has been visited by a heron recently and all my big Koi are spending all their time sucking at the waterfall. Is this a result of stress or a lack of oxygen?

Many thanks in anticipation of your advice.

Regards, Bob

Hi Bob,
If your pond is stocked on the high side, the activity of the heron is quite likely to have caused the fish some stress. They have produced a mass of ammonia in their anxiety and that has chased a lot of the oxygen out of the pond.
I dont know wether you are in the southern or northern hemisphere or how warm it is where you are. If it is hot, oxygen levels may be low anyway. If it is cold, there may be very little biological backup from plants or filtration to cope with any seismic changes in the environment.
So dont, whatever you do turn off that waterfall, and if they are still at it, I might suggest a partial water change of up to a third to dilute the ammonia pollution down. Whatever the problem this will help. Run the water in with force and from a height to help dissipate some of the chlorine and use lots of water conditioner to chase out the rest of the chlorine. Even if you cant get hold of pond water conditioner, tap water/ mains water is the less of two evils when it comes to chlorine versus ammonia.
Good luck
Pete