Ponds can offer a sense of joy and beauty. Incorporating certain pond features, be they decorative or functional, can provide breathtaking scenery or calming ambiance. When it starts turning green, it can become a murky and unsightly mess.

Just because it starts to turn green doesn’t mean it’s bad. In small amounts, algae in pond water are perfectly okay. It signifies a healthy pond ecosystem.

woman pointing at pond algae

Although each pond ecosystem has unique conditions, qualities, and characteristics, algae bloom becomes problematic when it is excessive. At this point, it is difficult to manage. Not impossible, only difficult.

This article will discuss what algae are and the common forms found in ponds or backyard water features. It will also explore the causes, prevention, solution, and control of excessive algae growth.

About Algae

Algae are a diverse group of eukaryotic photosynthetic life forms. But enough of the scientific jibber-jabber. The murky green look of your pond water is significant for an algae bloom. Dirty pond water may mean poor water quality, but green water doesn’t necessarily equate to being unhealthy.

Algae has a bad rep for causing aquatic life problems when it’s excessive. It reduces oxygen in the pond by preventing air from getting into the water.

It also feeds off the oxygen content of the pond water when there is no sunlight. This will lead to fish death in the pond. Also, the aesthetic look of ponds is greatly impaired when algae growth is not controlled.

Despite its bad rap, there are positives to algae growth in ponds. Planktonic algae represent the first part of the aquatic food chain. They get eaten by zooplanktons which, in turn, become fish food. In the daytime, algae produce oxygen for aquatic life through photosynthesis.

Common Forms of Algae in Ponds

There are two major types of algae you can find in your backyard pond or pond fountain. They include:

Suspended Algae


Suspended algae are often identified as green water. This is because it makes pond water appear green and cloudy. Suspended algae are single-celled algae that float on the surface of the water in a clustered and cloudy form. It is also referred to as the floating algae or pea soup.

Any imbalance in the water can result in suspended algae bloom. These imbalances could include light penetration, excess nutrients, or lack of proper pond filtration. All these can help the rapid reproduction of suspended algae.

Lower water temperature facilitates suspended algae bloom. At lower temperatures, aquatic life becomes less active, making algae the only organism contributing to the pond ecosystem.

Without competition for nutrients from fish and aquatic plants, the algae thrive. This is why suspended algae blooms occur in spring when the season starts to change.

String Algae

hand holding string algae from pond

String algae often attach to plants hanging on the rocks of pond fountains or waterfalls. These green algae can also hang on the water’s surface like a blanket.

Its long strands or filaments tangle together to form thick mats. Hence, it is also referred to as the blanket weed. These mats can double their weight in twenty-four hours.

As ugly as it appears on pond water, it doesn’t cause any significant danger to fish health. As long as it is under three inches, your fish are safe. Above it, it can impair your pond’s overall appearance and water clarity and reduce oxygen content.

String algae blooms occur during the same period as suspended algae bloom. But it can also occur during winter. Broken-down debris and organic matter from fish during their active season act as food sources for algae.

Without competition as a result of the cold causing hibernation, the algae can enjoy the nitrogen and phosphorus from them.

Other types of algae can be found in pond waters. Plant-like algae with a foul and skunky odor called musk grass, or Chara, is possible. The blue-green algae is another one. Also called cyanobacteria, the blue-green algae is especially toxic to both humans and livestock.

Controlling Algae or Green Water in Your Pond

Algae blooms are a natural phenomenon in water of all sizes. While it might seem daunting, algae control is far easier in smaller water bodies than in large ones. If you have a pond, be it a pond fountain, koi pond, fishing pond, or small lake in your backyard, you can control algae growth.

Pond algae control doesn’t mean getting rid of all the algae in your pond. Keeping the water clear is the goal, but algae have some advantages. Some fishes eat algae. Some fish feed contains algae. What you need is a balancing act. Ways to manage your pond ecosystem that is logical and consistent with nature.

Here are a few tips, tricks, and some of the best practices for a healthy pond ecosystem and algae control.

Proper Aeration

To control pond algae, maintaining good quality water is essential. One way to achieve this is aeration.

Whether it’s a decorative pond, a koi pond, a larger pond, or a small lake, aeration is bound to keep the pond water clean. Aeration prevents pond water from remaining stagnant.

When pond water is stagnant, dissolved oxygen floats to the surface. Low levels of dissolved oxygen lead to fish death. Aeration adds oxygen back to the pond water.

There are several choices when it comes to aerating your pond. Bottom diffusers are the best choice for fairly deep and deep ponds as it forces the water upwards for air. For shallow ponds, surface aerators like fountains work brilliantly.

It agitates the water and adds a spectacular touch of beauty to the whole setting. Bottom diffusers are necessary if your shallow pond freezes over during winter.

Proper Filtration

Filtration can help with water treatment. But before that, consider investing in a good old rake. Raking can help remove algae, debris, and muck. Yes, it is a bit of work, but how hard can it be?

It would take a few minutes at most for a small decorative pond or koi pond. Manually removing the algae is your best method, especially with string algae. Besides, it makes the filtration process easier.

An efficient mechanical filtration system can remove fish waste and pond debris.

Using Natural Pond Algae Controls

UV clarifiers are effective ways to eliminate discoloration in pond water. It destroys the ultra-fine particles responsible for discoloration.

Thus, they are great for ponds that are in open sunlight. Once destroyed, the dead particles clump to form pond scum. This pond scum is then removed by the mechanical filtration system.

Ionizers, especially copper ionizers, help keep pond water clear by depositing copper ions. It also reduces string algae buildups. Installation is easy as you can add them with plumbing or use a drop-in model.

Barley straw is an all-natural method for controlling algae growth. Barley straw does not kill existing algae but rather halts the growth of new ones.

During the decay of the straw, small but steady quantities of extracts are released. The extracts release chemicals inhibiting algae growth and improving pond water’s oxygen levels. Barley straw shows significant results when applied a year before the algae bloom.

Another natural method is the introduction of beneficial bacteria into the pond. Excess nutrients from overfeeding fish can cause an algae bloom.

These bacteria break down excess nutrients and organic matter into harmless gases. Thus, the algae are denied nutrients for growth. Beneficial bacteria are safe for both fish and aquatic plants.

Sunlight and Nutrients

Limiting the amount of sunlight and nutrients that gets to the pond water is an effective way of pond algae control.

Planting shade plants around the pond’s perimeter, adding floating plants, and installing waterfalls or fountains to circulate water are ways to prevent excess sunlight. Adding a pond dye can also prevent excess sunlight from penetrating pond water.

Avoid overfeeding fish, reduce the number of fertilizers used on lawns and gardens near ponds, and control run-off from farms or fields nearby. These are all effective ways to prevent excess nutrients from getting into your pond.

Chemical Treatment

Selecting the best pond algaecide and algae killer depends on the type of pond algae you want to treat. Algaecides are designed to destroy all algae forms, making them more effective. But extensive care is needed as algaecides can have detrimental effects on fish and aquatic life.

Algaecide does not directly cause fish death. The fish die as a result of lack of oxygen which was used up by bacteria breaking down dead algae. So, heavy aeration is needed after use.


Do you want to enjoy the tranquility of your outdoor space? Exercising pond algae control is a great way of keeping the aesthetic appealing.

Always try a chemical-free method first when dealing with algae blooms. It may take time, but it is the best way to maintain your pond ecosystem. After all, it’s a balancing act.

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