The distinctive brown hue of rivers and lakes around Pemberton, Western Australia, is primarily due to tannins—natural compounds released from decaying vegetation. As water flows through the dense karri forests and peat-rich soils characteristic of the Southern Forests region, it absorbs these tannins, resulting in the tea-like coloration observed in local waterways.

Understanding Tannins

Tannins are organic substances found in various plants, including the native flora surrounding the Southern Forests region. When leaves, bark, and other plant materials decompose, tannins leach into the soil and, subsequently, into nearby water bodies. This process is natural and contributes to the unique appearance of the region’s rivers and lakes.

Impact on Local Waterways

The tannin-stained waters are a hallmark of Pemberton’s natural environment. For instance, Lake Yeagarup, located within D’Entrecasteaux National Park, is described as a “young tannin-stained freshwater lake,” highlighting its characteristic coloration.

Similarly, the Warren and Donnelly River, which flows through the region, exhibits a brown tint due to tannins. If you are travelling through the region you may like to join one of the ecotours by boat or 4WD for further investigation into the waterways and their relationship with our forests. Watching these tannin stained waters reach the ocean can be mesmerising and seeing it mix with the sea brings out a myriad of colours. It is spectacular.

Ecological Significance

While the brown coloration might suggest pollution, here in our forests, these tannin-stained waters are typically clean and support diverse ecosystems. The tannins can reduce light penetration, influencing the types of aquatic plants and animals that thrive in these environments. However, many native species are well-adapted to these conditions, making tannin-rich waters an integral part of the local ecology.

Experiencing Tannin-Stained Waters – Can I Swim Here?

Step outside to one of the many streams, rivers and dams and you can see the golden copper hue of the waters running through our forests.

Swimming is not a problem, what you find is that the sunlight captures the warmth in the top metre of the water – so it actually is warmer than you may think! But put a toe into the cooler waters beneath this layer and you may think otherwise (its cold!).

It’s advisable to always exercise caution and adhere to local guidelines when swimming in natural water bodies. Keep an eye on the little ones and people who do not know how to swim, as the water is dark and the depth can often be unknown.

Understanding the natural processes behind Pemberton’s brown rivers and lakes enhances appreciation for the region’s unique landscapes. These tannin-stained waters are a testament to the rich biodiversity and ecological processes at play in Western Australia’s Southern Forests.