It is quite likely that you will have some growth of algae or duckweed in your pond at some time. This growth is natural and whilst it does not become excessive, there is no threat to your pond or its inhabitants. In fact there are species of beetles that spend their lives within duckweed fronds.

Should this growth extend to the stage where there is a minimal percentage of visible water surface, the balance of life in the pond may become unsettled. Blankets of weeds or algae occur due to an excess of nutrients, such as nitrates, in the water. The weed and algae grows aggressively on this rich food source and can eventually choke other pond life by blocking both sunlight and oxygen from reaching the water.

To tackle the immediate issue with weed or algal blooms, they can be physically removed using a rake, net, or any similar equipment. Having removed a significant manifestation of the problem, it is common for straw to be put in the water. The process of the straw breaking down produces a herbicide that kills the algae. Whilst these are effective methods for tackling the symptoms of the problem, real results will be achieved only once the underlying issue of nutrient rich water is tackled.

Nutrients can enter the pond from many sources such as fertilisers being washed in or the nutrients held within silt being disturbed. Common self inflicted issues could be a heavily stocked pond or excessive feeding. The heavily stocked pond will almost certainly have a filtration system to tackle pond polluting ammonia. A byproduct of that filtration process is nitrates. Excessive feeding is the equivalent of putting compost in your pond. A good practice is to remove uneaten food immediately and to also remove other compostable material such as fallen leaves from the water’s surface.

However nutrients have arrived in your water, a key activity for you, the pond owner, is to maintain a healthy balance in the water’s constituents. If you can manage the level of nutrients in the water, then the ability of weeds and algae to grow unchecked will be curtailed.