When your pond is established, you should find that, to an extent, the plantlife is naturally maintained by the pond animals which live in it.
Various creatures will keep the level of algae and blanket weed down by eating it for example. But with new ponds, which are yet to host the wildlife which can help keep things clear, you may find blanket weed quickly covers the water’s surface, especially in warm weather.
Either way, if you get a build up of floating weeds like this, you can carefully remove it with a stick or net. It’s best to leave the leave the weeds and algae by the side of your pond for a night or two, so that you can give any remaining creatures living in it the chance to escape back to the water!
Read more at the RSPB website.