What Causes Green Pond Water?

Whether you chose to have a pond to bring more wildlife to your garden or wanted a relaxing spot to while away the hours and watch your fish dart through the water, it can be unsettling to see your beautiful pond turn a shade of green. The good news is that you will not be alone in experiencing this, and there are some easy fixes. Green pond water is an extremely common issue for owners of garden ponds, fish ponds, and larger ornamental water features because of algae growth. Sunlight, excess nutrients, organic matter, and poor circulation can all contribute to this growth. 

If you have noticed your pond water is now green, this article is here to help, offering prevention and maintenance tips, as well as advice on when professional help may be required. 

Why Does Pond Water Turn Green? 

Pond water typically should be clear or colourless. If there is ever a bit of colour, it should be only a slight natural blue tint, nothing more. When you notice green pond water, it indicates suspended algae or algal blooms, often due to too much sunlight and nutrients. Throw in leaves, fish waste, and other organic matter, not to mention poor circulation and filtration, and these issues will only increase tenfold because you are feeding those nutrients natural fertilisers. 

Once you have noticed this, you will naturally want to act as quickly as possible to rectify it, but before you act, consider that treating the water may not resolve the underlying cause, and further investigation may be required to keep the problem from returning. 

What Causes Algae to Grow in a Pond? 

Algae is a microscopic single-celled organism that can grow and become visible within 24–48 hours within a pond ecosystem. The more sunlight it is exposed to, the faster it will grow, and when there are high levels of nutrients like nitrogen and phosphorus, these act as fuel for even more rapid growth. These high nutrient levels come from leaves, fish waste, and other organic matter. These alone can cause algae growth, but if you then have poor pond circulation or filtration, the problem can worsen, creating a stagnant, nutrient-rich environment in which algae will thrive. With such imbalances in pond conditions, before you know it, that colourless water will be anything but, and rapid algae growth will keep going until you seek treatment. 

For anyone with a fish pond, algae growth like this requires careful consideration in treatment and in maintaining the water quality fish need to survive, so make sure to reach out to experts for advice before moving forward. 

How Can You Prevent Green Pond Water? 

Your first thought will be, why is my pond water green? But the next thought that follows is usually, how do I prevent it from happening in the future? 

You should do the following: 

• Fish pond care should always start with how you care for your fish. Try not to overfeed them, as leftover food and excess waste can break down into nitrates and phosphates, essentially fertilising your algae. 
• As you turn your attention to the pond itself, begin with removing leaves, debris, and other organic material regularly. Aim to do this at least once a week, but ideally every few days during peak seasons like autumn, when leaves are falling in abundance. 
• Do not just look on the surface of the pond. For thorough algae prevention, you must check that your filtration and circulation systems are clear of leaves and debris. Try to clean your pump basket weekly and inspect the water flow. Monthly, aim to clean the filters using old pond water. Never use tap water for this. 

To stay on top of this cleaning and maintenance, you may find it useful to create a schedule, dedicating specific days to specific tasks to keep it manageable. Preventative pond maintenance may seem like a lot, but it is generally more effective than regularly treating algae once it has become truly established in your pond.  

Can You Clear a Green Pond Yourself?

Pond cleaning is achievable for a pond owner, but it should be treated carefully, especially in fish ponds. For the best outcome, follow our quick four-step guide to identify and learn how to clear green pond water to get pond algae control back:

1. Identify why your water is not clear. Is it debris or algae? Getting a sample is the best way to determine what you have. 
2. Remove debris such as leaves and dead plants from the pond and check the filtration systems. You will want to improve circulation. If it is just debris, you can move on to prevention steps, but if it is algae, continue with step three. 
3. Remove as much sludge as you can from the bottom of the pond using a net. Alternatively, you can use a pond vacuum. 
4. Reduce algae by manually removing as much as possible using a net. 

Once you have cleared your pond of algae and debris, you will need to test your water, potentially add a new aerator to push oxygen from outside the pond to the bottom of it, and get some aquatic plants that compete for the nutrients the algae love. 

When you have persistent or recurring algae and have to repeat the above steps constantly, this may indicate that the pond water quality is less than ideal and that there is an underlying issue with your filtration or the pond’s design. Calling a pond contractor is the most appropriate action to take when needing to clear a pond. 

When Should You Call a Pond Maintenance Professional?

While there are many times when you can clear pond algae with no issues, circumstances may require more specialist help. If, despite your best efforts, you are still looking down at persistent green or cloudy water, using a pond maintenance service is by far your best call. Pond specialists are highly skilled in water quality management, with a keen eye for identifying when there might be a problem with your pond filtration system or circulation, which can explain why your algae keeps returning so quickly after treatment. They will be able to assess the wider condition of your pond and address the underlying causes of the return. This way, they can tackle the cause rather than the symptoms.  

Of course, your issues may lie away from your systems. It could be that your pond is simply too big for you to comfortably manage taking care of it frequently enough, and you are starting to have concerns over the health of your fish residents and the quality of their water. If you have a particularly large pond with complex water features, fish pond maintenance experts can conduct their pond water treatment effortlessly. 

FAQs

Why does my pond water keep turning green?

Your pond water is likely turning green because of rapid algae growth due to overexposure to sunlight and nutrients from fish waste and leaves. 

How do I get rid of algae in my pond?

You can remove it manually using a net to scoop out the algae and debris, but you will need to take preventive measures to ensure it does not come back, including installing an aerator and not overfeeding your fish.  

Can poor filtration cause green pond water?

Yes, poor filtration is one of the leading causes of pond water turning green. When there is a lack of proper filtration in the pond, fish waste, uneaten food, and leaves can build up, releasing nutrients like nitrates and phosphates that encourage rapid algae growth. 

How can I prevent algae in a fish pond?

Where possible, try to give your pond as much shade as possible, as sunlight will encourage algae growth. Also, monitor how much food you are giving your fish, regularly clean and check your filtration and circulation systems, and remove any debris frequently. 

If you are experiencing recurring algae growth, poor water quality, or pond maintenance issues that leave you scratching your head, contact our Aqua Maintenance team today to get your pond back in action.