Understanding Pond Algae

Pond algae is not a problem in a well designed and maintained pond.  To achieve this it helps to understand a bit about pond algae, the types, the benefits of algae, what contributes to its rapid growth, and what you can do about it. Most people judge algae to be a problem based on aesthetics in situations where a pond is overgrown with algae.

What pond owners should consider more important is when algae growth threatens other aquatic plant and animal life. When a pond is in balance the aesthetic issue is not a problem.Don’t misunderstand, algae in ponds is perfectly natural and an important element for the overall health of a pond along with the many other interdependent plant and animal organisms that make up a pond ecosystem.

In general there are two types of pond algae; filamentous algae and planktonic algae. Both are very common and naturally occurring organisms. Generally you can tell the difference by sight because filamentous algae can cover the entire surface of a pond and planktonic algae commonly turns pond water a soupy color, typically green.  Be aware that algae can occur in many colors; green, brown, red, are common shades.

Pond algae, like any other plant, takes in sunlight, nutrients, and CO2 and gives off oxygen. So in small amounts it is good for your pond and serves as both a source of food and oxygen for other organisms in the pond. When the elements pond algae needs for growth get out of balance algae blooms rapidly and in large quantity compared to its surroundings.  This is the point where algae can go from being beneficial to being a problem.  A pond algae bloom can consume a large share of the basic elements needed by other organisms and result in choking off or killing both plant and animal organisms in the pond.

The situation varies by season but still relies on a change in one or more of the general conditions to cause an algae bloom.  These conditions are; increase in amount of sunlight, high pH level of the pond water, stagnant water, and increase in the amount of nutrients entering the pond. When faced with excessive growth of algae in a pond, the common first reaction is to ask ourselves what is wrong IN the pond? The source of the problem might actually be in the pond, but changing conditions outside the pond may be just as likely the reason.  So before determining a course of action to get  pond algae growth back under control take a step back and consider the surroundings of the pond.

Sunlight changes with the seasons and weather so the amount that falls on your pond is constantly changing.  During the mid summer the sun is high in the sky so there may be less shade on the pond during the day.  In fall and winter trees near a pond may drop their leaves and let a greater amount of sunlight reach the pond.  Maybe there have been changes in the landscaping near the pond that affect the amount of sunlight reaching the pond.

Nutrients enter a pond from many sources.  If runoff from other landscaping flows to the pond and fertilizer is applied to the landscaping nearby, then some of it will enter the pond.  There are many natural sources of nutrients such as leaves or other vegetation falling into the pond and decomposing.  Have ducks or other wildlife started to use your pond?  Ducks are notorious for using a pond as their bathroom and thus increasing the amount of nutrients entering the water. And of course in a fishpond the fish are being fed so the food and resulting fish waste are also contributing to the level of nutrients.

A high pH level may be the result of a number of events.  A change may occur in the water source for your pond.  Many nutrients bring with them elements that change pH levels. Another source to consider is the materials the pond is made of; some concrete, limestone and marble may leach elements that change the pH level of the pond.

Stagnant water can contribute to  pond algae blooms.  Depending on the water source, a pond may or may not have natural movement of the water.  Of course this can change with the season, it might also change due to mechanical breakdown in a pond pump, waterfall pump, fountain pump, pond filter, or other means of water circulation.

Rules for Designing a Pond to Minimize Pond Algae

• Position pond so it does not receive excessive sunlight during the year, in particular mid summer.
• Pond depth should be at least two feet, preferably more, to prevent sunlight from reaching the bottom of the pond.
• Build a pond out of proper materials that do not affect pH levels.
• Include a pond filter in the pond design to aid in controlling nutrient levels and water circulation.
• Design drainage around the pond to prevent run off containing fertilizers from entering the pond.
• Slope the bottom of the pond so vegetation that falls into the pond will collect at the deepest point make it a bit easier to remove periodically.

Control Algae in Existing Pond

• Maintain and care for the pond.
• Given time, ponds will find a biological balance so avoid excessive cleaning and water changes.
• Spend time to educate yourself on your specific situation and influences on your pond.
• Test your pond water for pH level.
• Add the right combination of aquatic plants to consume nutrients and block sunlight.
• Consider; water lettuce, water hyacinth, and water lilies.
• Cover about 60% of pond surface with plants.
• Include fish that feed on pond algae as part of their diet.
• Add a fountain or a waterfall to increase constant water circulation.
• If all else fails consider using water additives such as algaecides, bacteria, or UV sterilizer.

Whether you are planning a new pond or already have one; pond algae is a natural part of any pond and there are plenty of ways to handle it.  The best way is to help your pond find its natural biological balance and educate yourself on what influences this balance. Spend the time noticing the changes that take place in your pond as the seasons change so you’ll know when to consider making a change. So, be patient, enjoy the process of learning about your pond, consider both in-pond as well as out-of-pond influences on pond algae, make small natural changes of aquatic plants, fish, and other living organisms, monitor nutrient and pH levels, and as a last resort consider use of chemicals, UV sterilizers, or major re-building of your pond.