Blanket weed can make pond water murky and reduce its oxygen levels.
It is caused by the formation of algae brought on by too many nutrients in the water.
This can be due to a build-up of sludge on the bottom of the pond, fertilisers leaching into the pond or regular topping up with tap water.
Although chemical treatments are available it is often more practical to remove it manually.
Start by removing floating debris, and then remove the blanket weed by winding it gently around a long piece of timber.
This should be done at least once per annum.
The sludge on the bottom of the pond should be removed at two or three year intervals.
There are generally many water creatures residing in this sludge so in the interest of conservation it is best to save some of it in a container.
This should then be returned to the base of the pond when all cleaning and repairs have been done.
Each summer as a preventative measure, float nets of barley straw on the surface of the pond to reduce further infestation.
Use up to 50g per sq m of surface area, remove the nets when they turn black, usually after six months.