No matter if it is a decorative pond, water garden, golf course pond or stock tank, nothing drives pond owners crazier than an infestation of pond scum or pond algae. The only thing that equals the frustration of seeing it, is trying to control it. The ability to identify the type of algae in a pond and then to limit the nutrients available to it goes a long way in preventing pond algae growth.

There are 3 basic types of pond algae:

Planktonic algae are microscopic, free floating algae the give ponds their clear green color. A normal population of planktonic algae is mandatory for a healthy pond, as they are the base of the food chain and are responsible for supplying the pond with dissolved oxygen, essential for the health of the other aquatic life. When planktonic algae start to bloom, they will give ponds a pea soup coloration. This usually takes place in summer months.

Filamentous algae, often called pond scum or pond moss, begins growing on the bottom of ponds on surfaces like rocks and logs and resemble green fur. As the clumps grow, they break loose from the bottom and float to the top, causing ugly green mats on the pond surface. Filamentous algae begins growing in the early spring and is first noticed around the edges of the pond in shallow water. It has no redeemable value to a pond.

Attached-erect algae commonly are mistaken for a higher vascular plant due to its dense, gritty appearance and its resemblance to aquatic plants with leaf-like structures. Attached-erect algae are less common, but do to its thickness, blooms can be dangerous to swimmers along with being a nuisance to other water activities. Attached-erect algae provide no significant value to a pond system.

Algae blooms in ponds are stimulated by the availability of excess nutrients in the pond and sunlight penetration. Excess nutrients usually come from fish feces, decaying vegetation, fish food and fertilization run-off. Shallow, clear ponds are often the most likely environments for algae to occur, due to the ability of sunlight to penetrate through to the bottom soil.

The options available for algae control are wide. Herbicides/ algaecides like copper sulfate are common solutions used, due to its ability to kill the algae quickly. However, a quick kill off of algae will actually work against the health of the pond. Large algae kills will result in a decrease in available oxygen for other aquatic life and the increase in nutrients stemming from the dead algae, which leads to new cycles of algae.

A more sound and lasting approach would be to control the causes of the algae growth – nutrients, sunlight and oxygen.

Nutrient control involves limiting the amount of nutrients that enter that water that can feed algae. This can range from manually skimming debris and waste from the pond, physically removing the algae, installing an effective filtration system or limiting the number of aquatic inhabitants, but it should always involve the use of beneficial pond bacteria. Pond bacteria is crucial in breaking down and degrading all types of organic waste and should be used regularly.

Reducing sunlight penetration is a more difficult because you only have so much control over that, but a good pond dye and even the addition of aquatic plants can help to shade the water and limit the sun’s effect. A good rule of thumb would be 60%-70% coverage with plants.

Improving the oxygen levels in a pond can be done with a pond aerator or even a pond fountain. The infusion of oxygen will invigorate pond bacteria, making them more efficient at their job, while also keeping the pond water circulating (another deterrent to algae growth).

Effective algae control begins with knowledge and understanding of the type of algae you have and what causes the algae to grow. Once you have armed yourself with the proper information, treating the causes and controlling the sources become more manageable. Then, year after year, preventative maintenance becomes second nature and severe algae blooms become less and less of a concern.

For more details, visit this other Algae Control article.


Casey Coke is a Marketing Manager for Natural Environmental Systems, LLC, a global supplier of microbial solutions for pond and lake management. The company markets their own brand of pond supplies under the registered brand name of Pond Keeper.