Blanket weed is an extremely invasive form of algae growth that if left unchecked will choke your pond starving it of oxygen and eventually killing any pond life you may have in the pond. Once you have an infestation it is quite hard to eradicate although there are some preventative measures.
If you discover blanket weed in your pond one of the best forms of attack is to place a stick or garden fork in the blanket weed twiddle it around so the blanket weed wraps around the implement and then remove from pond (this can also be done by hand).
If you place the removed weed near the pond any little creatures trapped in the weed will be able to crawl back into the water. Discarded blanket weed is an excellent addition to your compost heap!
Garden Centres and Pond Centres do sell purpose made small bales of barley straw that can be placed in the pond and this can help prevent re-growth.
Blanket weed is more often than not a problem with new ponds where the eco system is yet to mature. Useful additions to your pond could include plenty of oxygenating weed and some surface cover plants like water hyacinths and water lilies.
If your pond is subject to lots of direct sunlight try shading it with large leaved plants of rigging up some sort of manmade shade such as a pagoda, this will help slow down the algae growth.
If you wish to try a chemical methods there are several chemicals available that you can add to your pond some on a weekly basis but these will need to be monitored very carefully to avoid an imbalance in the water.
Once your pond has become established you will find that infestations of blanket weed will become fewer and fewer and you will have that wonderful pond that can be enjoyed by all.