As it gets colder your pond plants will start to collapse as the Autumn begins. Frightening really that summer has gone so quickly!
As waterlily leaves begin to turn brown try and remove them from the pond so that they do not sink to the bottom of the pond and rot away down there over winter. In more Northerly areas it may soon be time to remove annual floating plants that will turn black in the first frosts and begin to decay in the pond water and continue to try and remove any duckweed you have so that it does not seed down onto the bottom of the pond only to reappear next Spring.
Iris foliage on the plants you have not recently been splitting up should be cut back and thrown onto the compost before they start to collapse, look tatty and rot down in the water.
Be prepared with the net to cover the pond – tree leaves will soon start to fall and the net should be across the pond in order to prevent them falling into the water, sinking and then rotting down over Winter. Put the net in place as soon as the first winds are forecast – the first windy night will bring down more leaves than you expect and you will have the job of having to remove them all – do it earlier rather than later! Some tree leaves take a long time to rot away and use up a lot of oxygen in the process.