Slime Algae on Backyard Ponds

24 May

Slime Algae on Backyard Ponds

Slime algae not just lower the aesthetic worth of the backyard pond but may also pose a threat to you and your pets. Some species of slime algae are not anything more than a nuisance, while others can cause severe health complications. Before you can control the slime algae in your backyard pond, then you must first determine what type of algae you are coping with.

Types of Slime Algae

The slime algae growing in your backyard pond is either green algae or blue-green algae. Green alga (Spirogyra) is a filamentous alga found close to the edges of lakes, ponds and ditches. This glowing green, mat-forming alga produces long strands covered in a slimy coating. Green alga is often known as pond scum and makes the body of water appear dingy and unattractive. It is generally not dangerous but may strangle small fish that attempt to swim through it or choke out desirable aquatic plants. Blue-green alga (Cyanobacteria) is a phylum of bacteria that cannot be seen with the naked eye except through an algal bloom. Blue-green alga can develop in almost any body of water containing freshwater and saltwater. Some species of blue-green algae release toxins which can threaten the life of domesticated animals, livestock and wildlife that drink from the polluted water. Although rare, blue-green algae can prove fatal to humans in addition to cause skin irritation and respiratory problems.

Chemical Control Approaches

Copper sulfate is one of the most common chemical controls of algae. Unfortunately, copper sulfate is extremely toxic to copper-sensitive aquatic life like snails, grass carp, trout and ornamental goldfish. Furthermore, the potency of copper sulfate to control algae depends upon the pH level of the pond water, and a water quality test should be conducted prior to applying copper sulfate to control filamentous and blue-green algae. Algaecides containing sodium carbonate peroxyhydrate won’t instantly kill the algae but may also inhibit its development and also help prevent a bloom from developing. Sodium carbonate peroxyhydrate is most successful when used as a prevention measure rather than a cure for slime algae — both green and blue-green algae — currently present from the pond.

Nonchemical Control Approaches

Research conducted in the United States and United Kingdom has shown mixed results for barley straw’s ability to control algae. According to the Ohio State University, barley straw will dominate filamentous algae — like green algae — with a ratio of about 0.025 lbs of barley straw a square yard of water. The decomposing barley straw releases a compound that can interfere with algae and also prevent fresh plant cells from growing. The Greene County Soil & Water Conservation District and the city of Lakeville, Minnesota, propose barley straw as a substitute for chemical control of blue-green algae. Purdue University states, however, that a field survey conducted by University of Nebraska found that when added to a lake that experienced past difficulties with blue-green algae — barley straw did not improve the water quality and blue-green algae nevertheless developed.


Blue-green algae blooms occur when the water remains, nutrients are high and temperatures are warm. These blooms usually disappear after a couple of days but can lasts for weeks or even months if the nutrients in the pond are extremely high. Because blue-green alga is visible during a bloom, water tests performed by a laboratory are the only way to understand if blue-green alga is present before the bloom begins. Until testing is finished, assume that the water is positive for blue-green algae and also take the necessary precautions to keep pets and people away from coming in contact with the water. To help prevent the growth of blue-green algae, reduce soil erosion and fertilizer runoff into the pond. This will reduce phosphorus from the water, which promotes algae growth. Adding plants in the coastline and bank of the pond will help filter runoff contaminating the river water.

See related