Why does the water in the garden pond foam?

Why does the water in the garden pond foam

The garden pond requires the right care to ensure that the fish and plants feel comfortable, and it becomes a haven for relaxation. Despite careful maintenance, foam may form on the water, primarily being an optical issue. This foam can have various causes and may be an indication that something is amiss with your pond. Most of the time, the foam is entirely harmless and does not harm the fish.

Natural and artificially formed foam in the garden pond

It is entirely natural for foam to form on the garden pond. It occurs due to the movement of the water, mainly in the morning hours, and typically disappears on its own. Naturally formed foam is often an indicator of a well-functioning ecosystem in your pond. It is mostly white but can be yellow when there is a lot of pollen present. If a significant amount of soil is introduced into the pond, the foam may take on a brownish color. Natural foam can result from the flocculation of protein or the enrichment of water with oxygen. You can recognize natural foam by various characteristics:

  • It may smell like earth or fish, depending on its cause.
  • It often contains small residues of plants, algae, or insects.
  • It frequently occurs after heavy rains and snowmelt.
  • It lingers if it forms due to the breakdown of organic matter.

However, foam can also form artificially when chemical substances like cleaning agents enter the pond. This foam sometimes has a perfumed smell and does not last long. In backlit conditions, the foam bubbles can display rainbow colors.

Causes of foam in the garden pond

The most common cause of natural foam on the garden pond is the movement of water due to wind. Foam formation becomes more pronounced the more the water is agitated. Strong water movements leading to foam formation are also caused by streams, fountains, and waterfalls. However, foam formation can have various other causes:

Introduction of surfactants into the garden pond

Surfactants can enter the garden pond through cleaning agents, detergents, or cosmetics, leading to foam formation. This can also occur when you occasionally remove stones from your pond and clean them with a cleaning agent. Even fertilizers that find their way into the pond can create foam through surfactants. Avoid using cleaning agents and fertilizers near your pond.

Foam formation due to limestone

Limestone placed in the water rarely contributes to foam formation. These stones enrich the water with oxygen, leading to the accumulation of bubbles on the water’s surface. Typical foam formation occurs when proteins are simultaneously dissolved. This foam is harmless and doesn’t necessarily need to be removed.

Saponins: Foam formation, mostly in spring

Saponins have a soapy smell and taste and serve a similar function to soap. They are present in aquatic plants and fish food and are a primary cause of foam formation, especially in spring. Saponins do not harm the pond inhabitants or the water; they can even support fish growth. Foam caused by saponins can result from excessive fish food. If it occurs excessively, you should remove it.

Foam formation due to proteins

A common cause of foam formation in the garden pond is protein dissolved in the water. The water contains numerous nutrients that flocculate due to natural water movement, resulting in foam on the water’s surface. This foam usually appears in the morning, is harmless, and indicates a well-functioning ecosystem. An increased foam formation due to proteins is often associated with a high nutrient input because these nutrients contain proteins. The causes of increased nutrient levels are:

  • Fish food
  • Fish excrement
  • Fallen pollen
  • Dead plant parts
  • Algae.

Imbalanced nutrient levels as a cause of foam on the water

If there is an excess of nutrients in your garden pond, increased foam formation may occur. A nutrient surplus often occurs in ponds with high fish populations in relation to the pond size. This leads to an excess of protein, resulting in increased foam formation. A surplus of nutrients can result from:

  • Fish spawn
  • Fish excrement
  • Dead animals in the pond
  • Fallen leaves and other plant parts entering the pond
  • Decaying plant material on the pond bottom
  • Algae
  • Overfertilization of shoreline plants
  • Phosphate and nitrate from neighboring agricultural areas.

You can prevent a surplus of nutrients in your pond by using high-quality fish food and not overdosing the amount of food. Additionally, remove algae, leaves, and dead plant parts regularly.

Issues with the filter

To avoid foam formation in your garden pond, the pond filter should always function correctly. When you install a new filter, it’s entirely normal for the water to foam. The filter requires a certain amount of time to break in. If the filter is positioned above the water surface, foam can form more easily as more air enters the water. The filter’s function is affected by deposits, so you should regularly clean it.

What you can do to address foam formation

Since it’s entirely natural for foam to form on the water, you cannot completely prevent it. If you know the cause of the foam formation, you can take appropriate measures. Regularly check the water parameters with test strips or drop tests, paying attention to the pH level, carbonate hardness, nitrate, nitrite, and ammonium. Foam catchers and float barriers are easy to use and are attached near the water surface. They capture the foam at the inlets and can be skimmed off.

Use a protein skimmer

A protein skimmer is installed directly in the filter. The water passes over several bio-rings and is aerated. Air and water remain in contact for an extended period, creating a surface tension. The resulting solid foam is separated from clean water in the skimmer and can be easily removed. A protein skimmer improves water quality by increasing oxygen levels and removing unwanted substances like phosphate, ammonia, or colorants from the water. The protein skimmer helps prevent algae growth.

Remove protein sources

Proteins are naturally present in every pond but can be prevented from being excessively released by eliminating protein sources:

  • Do not overfeed and provide only small amounts of food to avoid an excess of nutrients from unconsumed food.
  • Remove decomposed plant parts, pollen, and leaves that fall into the pond.
  • Regularly remove algae.
  • Especially in summer months, regularly monitor water parameters.
  • Clean the pond twice a year, in spring and autumn, and replace the water if necessary.

Ensure a functioning filter system

To ensure good water quality, it is crucial to have a functioning filter system. The filter must be regularly maintained and positioned correctly. Do not place the filter above the water level, as this would likely lead to increased foam formation. Water returning to the pond can become overly oxygenated. If you install a new filter, expect a break-in period of about a week when foam can still form. You can improve the filter’s performance by using pond starter bacteria in the filter.

What to consider during water changes

If surfactants have entered the pond, you should perform a water change. Remove as much foam as possible and exchange a large portion of the water. Allow the pond pump to run for some time to remove any remaining surfactants. If there is a threat from the surroundings, also stop external inflows.


Foam formation in the garden pond cannot be entirely prevented and is typically not harmful. Dissolved proteins and water movements lead to foam formation, which naturally disappears and indicates a well-balanced ecosystem. Foam can affect the pond’s appearance. To avoid unnecessary protein input, feed your fish in moderation and regularly remove contaminants from the pond. Ensure your filter system works well. You can use foam catchers and protein skimmers to remove excess foam.

Florian Egert

I am Florian Egert, the owner of pondlovers.com. I live with my wife and two children in Germany in a small village in the countryside.

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