String algae looks like a lot of filaments hanging onto rocks and any rough surface. It can double its weight in a day, can become partially detached, float to the surface and can spoil your pond's look and feel.
This type of algae has a tensel strength when pulled away from rock, making this task very difficult.
It also loves waterfalls and shallow water, growing from the bottom and edges of your pond. The main reason that it gains a foothold is lack of circulation in these areas of the pond.
Don't confuse this algae with the soft gelatinous type found on the pond sides.
This form of algae is beneficial and its presence is a sign of a balanced pond.
Unfortunately, where you have a pond that you can enjoy, you will have this problem. The conditions that lead to algae are mainly warm temperatures, sunlight, nutrition in the form of plants and leaves that decay in the pond, over feeding your fish and, if you have too many fish, the fish waste itself can lead to algae growth. High ph value is also another promoter of algae.
One of the absolute worst of the algae plants is known as blanket-weed, which is resistant to UV light. It literally starves the rest of the algae out of the pond by keeping the sunlight out of the pond.
Improving the pond's balance is one way to control blanket-weed.
Keeping your fish population to a manageable level will help control the algae.