Blanket weed, thread algae, string algae and filament algae are common names for a variety of different species of filamentous algae.
Blanket weed is very often seen clogging pond filters and entangled with pond plants. It grows in dense green masses and quickly becomes an unsightly nuisance if steps are not taken to control its growth.
Algae are a normal part of the ecology of ponds, will always occur, and are to some extent necessary for a healthy pond. An excessive growth of algae however can be detrimental and very unsightly.
The quantity of algae in your pond will depend on the weather, the amount of sunlight penetrating the water, the temperature of the water, the concentration of oxygen in the water, the amount of nutrients present and the number and variety of plants present.
Algal growth is likely to be at its worst in the spring when water temperatures and sunlight are on the increase and the plants are still struggling to recover from winter. In time the plants may flourish again and the situation may improve.