Microplastics are a global problem, infiltrating all levels of food systems and ecosystems. Now a multi-level governance issue, reaching across international, national and local scales, microplastics are most known for their impact on oceanic ecosystems, however, freshwater ecosystems are equally significantly impacted by plastics. Microplastics have been noticeably less researched in freshwater ecosystems compared to marine environments, with less than 4% of microplastic research looking at freshwater systems. With limited research looking into freshwater systems, Australia’s native fish are being overlooked.

So, what are microplastics and why are they bad? 

Plastic is a significant part of our everyday lives. We use it in almost everything we do. According to the Australian Department of Climate Change, Energy, Environment and Water, Australians used 3.4 million tonnes of plastics in 2018-19, and it is predicted that plastic use across the world will double by 2040. By 2050, it’s likely that plastic in our global oceans will outweigh the biomass of fish. 

Microplastics, as defined by the US National Ocean Service, are small plastic pieces – less than five millimeters – which are harmful to our aquatic life. They often are broken down from larger pieces of plastic, and can come from products as every-day as toothpaste, clothing and water bottles. Plastics and microplastics are particularly harmful, because unlike many other molecules and toxins, they break down and decompose incredibly slowly, over a time frame of thousands of years. They are not only in the natural environment but have also entered all parts of the food chain and have been found in many different types of animals.  

There are two types of microplastics recognised in the scientific community: 

  • Primary microplastics are originally manufactured to have a size smaller than 5mm. These are often in personal care products, textiles and medicines.   
  • Secondary microplastics are fragmented debris from larger plastic items, like plastic bottles, takeaway containers, and other larger plastic objects. The majority of microplastics found in the environment are fragmented secondary microplastics.


Microplastics are known to threaten biodiversity and human health in two ways. Scientists have found microplastics are causing physical harm to smaller animals that ingest microplastics, such as cutting their mouths or filling their stomach, making feeding almost impossible. Microplastics are also believed to transport harmful chemicals into the food chain, which eventually are ingested by both animals and humans, however, the exact effect of these chemicals remains a mystery due to the long timeframe plastic degradation operates within.  

Other effects are still being researched, however, studies have indicated that microplastics cause a variety of toxic effects to fish who ingest the materials. These could include:

  • Inhibition of growth and development
  • Impacts on feeding, behaviour and reproduction
  • Damage to immune systems and genetic material.
  • Other possible consequences involve microplastics accumulating in the tissues of fish and potential impacts at a molecular level, however, these a more common with nanoplastics, which are smaller than microplastics.
A Rainbow Runner in the North Pacific Gyre that had ingested 18 pieces of plastic (2008). Credit: Dr. Marcus Eriksen Gyres Institute

Are freshwater fish being left behind?

While the image above is an oceanic fish found with plastic inside it, more and more studies are showing that freshwater fish and other terrestrial organisms are not exempt from the intrusion of microplastics. 

Although inland rivers and lakes do not witness the immense amounts of plastic rubbish seen in marine environments, like the Great Pacific Garbage Patch (below), microplastics have been recorded and freshwater systems are likely an entry point before microplastics end up in the ocean. It is also known that big environmental events, like the major floods we have recently seen throughout south-eastern Australia, are prone to dislodging trapped microplastics. These floods release microplastics into the freshwater system where they can be ingested by fish and other aquatic creatures. Now more than ever, we need research looking at microplastics in native fish in Australia. 

The Great Pacific Garbage Patch is filled with plastics and microplastics with long lifespans. Credit: The Ocean Cleanup.
Credit: National Geographic

Where to from here

There are clean up groups globally and locally who have realised the importance of reducing microplastics and other rubbish that enters freshwater rivers. Some of these include the Ocean Cleanup and the Yarra Plastic Paddle. Major cities, like Melbourne and its Yarra Plastic Paddle, are leading the way on the issue of plastic pollution as they are major sources for microplastics that end up in rivers. 

Despite a recent focus on this issue, there are still major knowledge gaps about the impact of microplastics on terrestrial and freshwater ecosystems and their food chains. Australian freshwater ecosystems need more research about microplastic intrusion, especially looking at the impacts on native fish and what sort of mechanisms will reduce those impacts. 

Ultimately, microplastics are a result of human consumption. There are several ways to reduce their impact on the environment, both freshwater and oceanic, however, the easiest action is to reduce the amount of plastic we use everyday, and dispose of the plastic we do use thoughtfully – into a bin. However, this extends beyond the capacity of individual consumers. Governments, at all levels, needs to take the initiative to regulate plastic use and disposal. Corporate responsibility also plays a role in this. Businesses that use plastic in their products must look at where their plastic ends up, and ensure they are recycled, instead of entering the mouths of native fish in our rivers and oceans.

Research in the space:

Check out this video on the lifecycle of the Majestic Plastic Bag

Main photo: Secondary microplastics found on a sandy beach.

Credit: Geographical. 

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