If your pond has duckweed floating on the surface at the moment you should try and remove this now before it drops its spores to the bottom of the pond. These spores will rise as the water warms again next year to invade you again in Spring with another crop of duckweed.
Although duckweed is a surface cover plant that keeps the green algae and blanketweed at bay it is such a vigorous spreading plant that it is hard to control and will very often become a problem in its own right. It can completely cover the surface of the water with a carpet of growth that will block out all light to the submerged plants beneath the water. These will then die off leaving rotting vegetation and no source of oxygen for the wildlife or to complete necessary biological processes.
It is not ideal as a surface cover plant as there is no effective control mechanism for it. Taking it out with a net can be time consuming and soul destroying as it seems to reproduce as quickly as you remove it and see a space in the water. Underwater creatures are happy to have some duckweed as cover to hide under – the question is how to control how the amount stays at a reasonable level.
Control now means less problems are likely next Spring.