The British Native oxygenating plants that had dropped down to the base of the pond for protection against frost and ice are starting to regrow but you will not see them near the top surface yet. The top inches of your pond water may feel warmer to you but it takes some weeks of sunshine before the warmth penetrates deep into the pond water and warms it sufficiently to make the submerged plants respond. They have not died and will return. The Non Native oxygenators may have stayed nearer the water surface and could be mushy by now if they were caught in a layer of ice.
Ceratophyllum demersum(Hornwort) is the best all rounder of the Native oxygenators as it continues to work well all Winter – some others will reappear later once the risk of frost and ice is over. See our Tips and Advice – Oxygenators, Seasonal availability page for more details.