Cover the surface of ponds with netting to stop fallen leaves from entering. Accumulated debris in the pond can encourage growth of algae and weeds, which will eventually harm the fish by reducing available oxygen levels.
Top up water levels when necessary, particularly during warmer weather, and continue to remove blanket and duckweed.
Remove dead leaves from waterlilies as the foliage dies back. Now is also a good time to divide waterlilies and other pond plants to increase stocks or control over-vigorous growth.
Overgrown marginal plants can just be cut back, if further stocks are not required. A maximum of 50 percent of the water’s surface should be taken up with planting.
Troubleshooting
Waterlilies can be prone to fungal problems such as crown rot and leaf spot, so nip any problems in the bud by dealing with them promptly. Remove affected leaves, reduce watersplash from fountains and, if necessary, repot the whole plant in fresh compost after first removing all rotten looking bits of root, stem and leaf.
You may need to thin out submerged oxygenating plants, as they can quickly build up and crowd the pond.