How To Fix Green Pond Water

Green pond water is something that just about every pond owner experiences at some stage.

When your pond turns green, it’s a sign that the pond’s ecosystem is out of balance.

There are many natural ways to clear pond water, so you don’t have to take drastic action like draining your pond or using harmful chemicals.

Here are some easy ways to get rid of murky, green pond water naturally.

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A note for new pond owners:

If you’ve just installed a new backyard pond and the water has turned green, don’t be tempted to drain the pond.

It takes time for the good bacteria to build up in the pond, so if you drain the pond you’ll just have to start over.

You can help it along by adding natural beneficial bacteria to your pond.

As the good bacteria reproduces you’ll notice that the algae will decrease and you’ll get less algal blooms over time.

You can also try a product called pond enhancer, which contains natural bacteria along with a blue dye that is safe for fish and helps to shade the pond so the algae don’t receive as much sunlight to grow.

pond water

What causes ponds to turn green?

Green pond water is caused by an overgrowth of algae suspended in the water.

Algae becomes overgrown when nitrate and phosphate levels in the water are high.

What leads to an imbalanced pond ecosystem?

green garden pond

Plant matter

Leaves, dead plants and lawn clippings that fall into the water decompose and form sludge.

When sludge and muck builds up on the bottom of the pond, it releases nutrients into the water which provides food for algae to grow.

green lily pond

Too many fish in the pond

Fish waste breaks down into nitrates that algae feed on.

Many people buy too many fish for their pond, not realizing that they reproduce quickly.

Goldfish reach sexual maturity at one year of age and they can spawn up to five times a year during the warmer months. [1]

Koi are fast growing fish and spawn in late spring to early summer.

It doesn’t take long for a small pond to become overrun with fish, so you may need to sell or give away some of your fish.

Fish pond

Overfeeding Fish

If you’re feeding your fish too much, the uneaten food will rot and produce food for algae.

Scoop out any uneaten fish food and reduce the amount of food if it’s being left uneaten.

Feeding your fish less will also give the fish an opportunity to eat some of the algae.

Not enough plants in the pond

Pond plants help to reduce algae because they consume nitrates and phosphate in the water, leaving less nutrients available for the algae to grow.

green pond with bridge

How to get rid of green pond water

Clean the pond regularly

If you have a large pond, you can install a pond skimmer that will remove any leaves or debris that falls into the pond or get into a routine of regularly scooping out any plant matter that falls into the pond.

Use a long handled net to remove the muck and sludge that builds up on the bottom of the pond or use a pond vacuum to suck up the sludge.

Another way to reduce the sludge is to add muck reducer tablets to the pond to help break down the sludge naturally.

These tablets contain beneficial bacteria and they’re safe for pond fish.

murky green pond

Add aeration

Aerating your pond with a fountain, pond spitter or waterfall increases the growth of aerobic bacteria that are beneficial for reducing built-up waste in the pond.

Install a UV clarifier

UV clarifiers use ultraviolet light to destroy algae that is suspended in the water.

Using a UV clarifier is an effective way to remove heavy algae blooms in as little as five days and keep your pond free of algae overgrowth in the long term.

green pond with plants

Increase the number of pond plants

Plants compete with algae for nutrients in the pond, so include some floating plants like water hyacinths or water lettuce (check that they’re not banned in your area), along with some marginal plants like lotus and water lilies.

Reduce the number of fish

De-stocking your pond will help to reduce algal blooms and give your fish more space to swim around.

small pond with green water

Common Questions

Is green pond water dangerous for fish?

A small amount of algae is normal in a healthy pond and fish will eat the algae, but when algae becomes overgrown, oxygen levels in the pond fall quickly, which can lead to fish kills.

a beautiful pond with an algae bloom

How long does it take to get rid of green pond water?

Depending which method you choose, it can take a few weeks to a month before you start noticing your pond water clearing. Using a UV clarifier will speed things up though.

So there are my tips for clearing green pond water naturally.

green pond stream

Algae overgrowth is one of the most common problems for backyard pond owners but by following the tips in this article, you should be able to get on top of the problem in a short amount of time and have a healthy, balanced pond ecosystem.


What do you do when your pond turns green? Let me know in the comments below.

Are you on Pinterest? I have boards dedicated to Garden Ponds and Pond Tips that you may find helpful.

Don’t forget to pin this post so you can come back to it later.

clearing algae from a pond
How to fix green pond water

Kelly Martin

Hi, I'm Kelly Martin, a landscape gardener with a special interest in ponds and water gardens. For over a decade, I've been designing and creating beautiful gardens that feature stunning water features, from small garden ponds to large water gardens. Read more

This Post Has One Comment

  1. Brad Mildern

    I have a 1000 litre pond only a foot deep and 3 metres by two. It has overhanging trees (Mango’s) and plenty of water plants. (Mustard and papyrus). I have four Koi and about 14 goldfish (Rockets). My pond goes green at least once per month. I have a pool sand filter augmented by a sump pump capable of emptying the pond in ten minutes or filtering it in about a day of operation, but the sand filter requires back flushing every 15 minutes because it gets so foul and the detritus pre-filter on the intake gets clogged. With that amount of back flushing of the filter I waste about half the pond water anyway and so have to top it up with a hose. The fish love this and congregate under the hose spray to get more oxygen. The filtering is a LOT of work and time and should be done at least every few days. It cant run permanently as it clogs in 15 minutes.. One tip… A bag of clover or barley hay over the inlet pipe introduces good bacteria which cuts algae growth by about 50%

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