New season's Koi will be ready for introduction from mid March. The season for aquatic plants starts properly from mid March when most of the frosts are over. However, it is worth leaving some protection in case of late frosts. Revive straggling Elodea by cutting 10cm cuttings and replanting in gravel in a basket. When repotting lilies it is important that the crown of the rhizomes is exposed to the water not smothered with soil or gravel.
Lilies prefer a warm sunny spot.
This is particularly so in ponds made of liner where standing in the pond could cause damage.