Is Mustard Algae Dangerous?

Is Mustard Algae Dangerous? Can I Still Swim In The Pool?

Mustard algae is a strain of algae that commonly occurs in natural bodies of freshwater in areas with warmer climates. Like all algae infestations, it can have potentially harmful effects for swimmers when it is introduced to your pool, but you may be wondering: is mustard algae dangerous?

In this article we will talk about the potential dangers of mustard algae infestations, as well as other reasons that we recommend that you avoid swimming in pools with mustard algae.

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Is Mustard Algae Dangerous to Swim In?

Mustard algae, sometimes referred to as yellow algae because of its colour, is nontoxic to humans. However, even though the algae itself is not dangerous, overgrowths of any type of algae are known to provide breeding grounds for other bacteria in your pool.

In saying this, if you are maintaining adequate levels of free chlorine in your pool and are circulating your water through the filter for a minimum of 8 hours each day, it is unlikely that dangerous amounts of bacteria will develop, even with an ongoing mustard algae infestation.

This is because mustard algae is highly resistant to chlorine, especially when compared to other organisms like bacteria.

So although mustard algae in your pool may survive normal chlorine levels, and can even survive some of the highest-strength shock treatments, it is extremely unlikely that any significant amounts of harmful bacteria will develop in these conditions.

Although swimming in a pool with mustard algae is technically safe so long as your chlorine levels and water circulation are adequately maintained, there are other reasons that we recommend you avoid swimming in pools with mustard algae.

Why You Should Avoid Swimming In Pools With Mustard Algae

Mustard algae may not be the most dangerous type of algae to have in your pool, but it is one of the hardest types of algae to get rid of.

This is due to its uniquely high chlorine resistance and its loose, powdery texture. Where other algae growths are slimy or may resemble a more stubborn, moss-like texture, mustard algae quickly scatters into clouds of dust when it is disturbed.

These tiny cells of mustard algae dust can survive even once they have dried out, so any of this algae that ends up on your bathing suit or other swim equipment can be reintroduced to your pool and cause new infestations at a later date.

As these spores can remain viable when dry, they can also cause contamination in any other pools where the same equipment is used.

It can be complicated to clean this type of algae off of swimwear and other pool equipment, so we recommend that you avoid swimming in pools with mustard algae altogether.


Is mustard algae dangerous? The short answer is no, mustard algae is not dangerous by itself. However, that does not mean swimming in a pool with mustard algae is always a good idea.

If you must swim in a pool with mustard algae, it is important to ensure the chlorine levels are adequately maintained to reduce the risks of related bacterial growths. Use a chlorine calculator to help calculate dose rates, and consider adding a mustard algae algaecide.

Do you have any questions about the dangers of mustard algae? Let us know down in the comments, we’d love to help!

Louis from Pool Advisor


A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.