What Is Pond Scum and How Do I Get Rid of It?

If you've ever owned or managed a pond, you've probably encountered pond scum at some point. It's that unattractive layer of algae or floating organic material that sits on the surface of the water, turning your once-beautiful pond into a murky, green mess. But what exactly is pond scum, what causes it, and—most importantly—how do you get rid of it?

In this post, we're going to explore pond scum in depth, covering the causes, prevention methods, and the most effective treatment options available. By the end, you'll have a clear understanding of what pond scum is, how to stop it from forming, and how to remove it if it does.

What Is Pond Scum?

Pond scum refers to a layer of floating algae, organic matter, or bacteria that collects on the surface of ponds, lakes, and other bodies of water. It's often caused by a combination of excess nutrients in the water, sunlight, and stagnant conditions. The most common form of pond scum is filamentous algae, also known as "string algae," which forms dense mats on the surface of the water.

Pond scum can range in color from green to brown to yellow, depending on the types of algae or organic material present. While it might seem like just an aesthetic problem, it can actually be harmful to your pond’s ecosystem, blocking sunlight, depleting oxygen levels, and creating a breeding ground for mosquitoes.

What Causes Pond Scum?

The main culprit behind pond scum is an overabundance of nutrients in the water, primarily nitrogen and phosphorus. These nutrients can come from a variety of sources, including:

• Fertilizer Runoff: Fertilizers used in landscaping and agriculture can wash into your pond during rain, carrying high levels of nitrogen and phosphorus that promote algae growth.
• Decaying Plant Material: Dead leaves, grass clippings, and other organic matter that fall into the pond break down and release nutrients that feed algae.
• Fish Waste: If your pond has a fish population, their waste adds to the nutrient load in the water.
• Poor Water Circulation: Stagnant water creates the perfect environment for algae and bacteria to thrive, especially in the warm summer months.

How to Get Rid of Pond Scum

Once pond scum has taken over, it can be challenging to remove without the right approach. Luckily, there are several effective treatment options for eliminating it.

1. Manual Removal
   If you have a small pond, the first step is often manual removal. Using a rake, skimmer, or net, you can physically remove the algae mats from the water. While this is only a temporary solution, it can help reduce the severity of the problem.

2. Aeration
   Poor water circulation is a major factor in pond scum formation, so adding an aeration system, such as a fountain or circulator, can help. Aeration keeps water moving, distributes oxygen, and prevents stagnant conditions that algae love. It’s especially effective when paired with other control methods.

3. Beneficial Bacteria
   Adding beneficial bacteria to your pond is a natural way to control algae growth. These bacteria consume the excess nutrients that algae feed on, starving the scum before it can take over. Beneficial bacteria treatments are safe for fish and plants, making them an eco-friendly solution.

4. Algaecides
   If you're dealing with a particularly severe case of pond scum, algaecides can offer a more aggressive treatment. These chemical solutions kill algae on contact, but they should be used carefully, as they can harm fish and plants if over-applied. Always follow manufacturer instructions and consider a fish-safe formula if your pond is home to aquatic life.

5. UV Clarifiers
   UV clarifiers use ultraviolet light to kill free-floating algae cells. While they won't remove large mats of string algae, they can prevent the water from turning green by keeping algae levels under control.

6. Barley Straw
   Barley straw is a natural pond treatment that has been shown to help control algae. When barley straw decomposes in water, it releases compounds that inhibit algae growth. Barley straw can be added to the pond in small bales or as an extract.

Preventing Pond Scum

Prevention is always better than treatment, so once you've cleared your pond of scum, there are several steps you can take to keep it from returning:

• Limit Nutrient Runoff: Be mindful of fertilizers used around your pond. Opt for low-phosphorus formulas, and consider installing a buffer zone of plants around the pond to capture excess nutrients before they enter the water.
• Remove Debris Regularly: Skim the surface of your pond frequently to remove leaves, grass clippings, and other debris before they break down.
• Install an Aeration System: Keeping water moving is one of the most effective ways to prevent pond scum. An aerator or fountain can maintain healthy circulation, preventing algae from forming.
• Use Pond Plants: Aquatic plants like water lilies or duckweed can help absorb excess nutrients, competing with algae for the resources they need to grow. Plus, they offer shade, reducing the amount of sunlight algae receive.

Is Pond Scum Harmful?

While pond scum is often more of an eyesore than a serious threat, it can have negative effects on your pond's ecosystem if left unchecked. Thick mats of algae block sunlight from reaching submerged plants, disrupting photosynthesis. This can cause oxygen levels in the pond to drop, especially at night when algae consume oxygen. Low oxygen levels can lead to fish kills and create a stressful environment for aquatic life.

Additionally, certain types of algae, like blue-green algae, can release toxins that are harmful to both animals and humans. If your pond water looks unusually cloudy or has a strong, unpleasant odor, it's a good idea to test the water and take action quickly.

Conclusion

Pond scum can be frustrating to deal with, but with the right approach, you can restore your pond to its clear, healthy state. Whether you choose manual removal, aeration, beneficial bacteria, or algaecides, understanding the causes and treatments for pond scum is key to long-term success. Preventive measures, like reducing nutrient runoff and installing an aerator, can help keep your pond scum-free and thriving for years to come.