Start feeding the fish. Little and often is best, to prevent excess food leading to unwanted algal blooms. Frogs, toads and newts begin to spawn as the weather improves.
Remove pool heaters when the weather starts to warm. Clean out pond filters. Replace pumps, water features and lighting systems, after checking they are in working order.
Remove netting coverings placed over the pond to protect it from autumn leaf fall.
Begin dividing marginal and bog garden plants if overcrowded. Contain vigorous perennials by planting in aquatic plant baskets and top with a layer of gravel to prevent fish stirring up the compost. Cut back old marginal vegetation from around the pond.
Tidy up plants in the bog garden and mulch with composted bark (or similar material).
Troubleshooting
New or recently cleaned ponds can suffer problems with algae. Providing some shade can help reduce this problem, and site selection can be crucial here. Ironically a covering of Lemna (duckweed) can provide sufficient shade to help suppress the algae until cultivated aquatic plants establish sufficiently to suppress the duckweeed’s proliferation.
Other helpful measures include filling the pond with rain water rather than tap water, avoiding getting soil or compost in the pond (as these contain fertilisers that encourage algal growth), and taking care to remove plant debris from the water promptly.