Waterways can look different from day to day. This guide helps explain some of the natural features you might see in our local creeks, streams, and wetlands.
Clear water
Photo: An example of clear water in a waterway.
Clear water has less dissolved and suspended material.
Mountain creeks are often clear because they run over bare rock without sediment or vegetation.
Shallow water also tends to be clear because there is not enough depth for the long, blue wavelengths of light to travel and be reflected.
Clear brown or reddish water
Photo: Clear brown or reddish water in a waterway, sometimes water is clear but brown like tea.
The colour is the result of dissolved organic material from the breakdown of plants and animals.
The material leaches into slow moving streams and lakes from surrounding forests, and wetlands, and stains the water brown or reddish brown.
Turbid water (sometimes grey or brown)
Photo: An example of turbid water in a waterway.
Turbidity in open water may be caused by growth of phytoplankton.
Human activities that disturb land such as construction can lead to high sediment levels entering water bodies during rainstorms due to storm water run-off.
Areas prone to high bank erosion rates as well as urbanised areas also contribute large amounts of turbidity to nearby waters, through storm water pollution from paved surfaces such as roads, bridges, and parking lots.
Slime or fluff (Iron bacteria – orange slime and fluff)
Photo: Orange slime in a waterway.
Orange, rusty coloured slime or fuzzy material in a waterway is often caused by iron bacteria. These naturally occurring microorganisms use iron in the water as an energy source and can create:
• Rust coloured slime or deposits
• Orange or brown “fluffy” material
• An oily looking sheen on still or slow moving water
• A metallic or musty smell
As iron bacteria grow and reproduce, they excrete slimy or fuzzy material. This material often becomes coated with rusty iron hydroxide, giving it the distinct orange colour. Iron bacteria can also create natural oily sheens.
Iron bacteria are harmless to people, animals and the environment.
In some areas, iron‑rich groundwater may seep to the surface. When the iron in the water is exposed to air, it can form an orange crust or stain on rocks or surfaces. This crust is usually not fuzzy like the bacterial growth.
Why it appears
Iron bacteria thrive in water that has:
• Slow movement
• Low oxygen
• Naturally high iron levels
These conditions are common in stormwater outlets, wetlands, and groundwater fed creeks.
Identifying oily sheens
Iron bacteria can create an oily sheen similar to petroleum.
For help telling the difference, see the Oily sheens section further down this guide.
Algae
Green hair-like strands and green clumps are formed by filamentous algae. These colonies of microscopic plants live in shallow water on the bottom near shore or on submerged objects.
Blue-green algae can present like a paint-like presence or strong colour in the water.
Blue-green algae can pose a health risk to humans and animals. If you suspect you have an algae bloom do not drink the water.
More information from the NSW Department of Primary Industries:
Farm water quality and treatment: Algae
Should I be concerned about algae?
The presence of algae in a waterway does not necessarily mean the water is polluted.
A diverse community of algae is healthy. Algae are an important source of food and oxygen for other plants and animals in the water.
Sometimes, certain conditions might favour a species that is normally rare in a waterway. With the right temperature, light, and nutrients in the water, the rare organism might multiply rapidly, forming a bloom.
When an algae bloom is persistent or occurs routinely, too many nutrients may be entering the water. Nutrients, especially phosphorus, fertilise a waterway just as they fertilise your lawn or garden, causing microscopic plants in the waterway to grow.
Identifying algal blooms
WaterNSW has information to help identify different types of algae in waterways.
WaterNSW Algae Alerts Map
NSW Health Recreational Water Quality
WaterNSW Algae Contacts
Plumber’s Dye / Phosphorescence
What is Plumber’s Dye?
Plumber’s dye is a coloured, water‑soluble dye used by plumbers, contractors, and councils to trace water flow and detect leaks in pipes, drainage systems, and storm water networks.
Examples of Blue dye (plumber’s dye test)
Examples of Green dye (fluorescent tracer)
Is it harmful?
No. Plumber’s dye is non‑toxic and safe for people, animals, and the environment.
Why it may be reported
Although harmless, the dye can temporarily colour water a bright or fluorescent shade. This can look like pollution, so if you see unusual coloured water, please report it to The City of Coffs Harbour so we can check the source.
What The City is doing
The City also uses dye testing to help identify illegal storm water connections to the sewer system.
For more information, visit our Stormwater Inflow Reduction | City of Coffs Harbour page.
Pollen, oily sheens, and foam
Pollen
A yellowish powder or dust on the surface of water in spring and early summer is probably pollen from trees.
Pollen can also collect in clumps or blobs.
After becoming water-logged, the pollen sinks to the bottom or may collect in shallows along the banks. Lines of pollen may be left on rocks as water levels drop.
Oily sheens
Photo: Natural oily sheen fracturing when broken with a stick.
An oily sheen that reminds you of rainbow puddles in an asphalt parking lot might be from spilled petroleum.
A minor spill is usually enough to form a film across the surface of large waterway.
Oily sheens can also come from natural sources. Some bacteria (Leptothrix discophora) that live in waterlogged places get their energy from iron and manganese, and as these harmless bacteria grow and decompose, the iron may appear oily or form red or orange films, fluffs, and coatings.
What is the difference between petroleum spills and natural oil sheens?
Photo: Natural oily sheen fractured and brown fluffy evidence of iron bacteria.
Test: Poke the sheen with a stick.
If the sheen swirls back together immediately, it's petroleum.
If the sheen breaks apart (shatters or forms many sided fragments) and does not flow back together quickly, it is from bacteria or another natural source.
Foam
Photo: An example of foam in a waterway.
Foam is often seen along lake shores and on streams and rivers. Most foam is natural and does not indicate pollution.
Foam forms when water is mixed with air, such as by a waterfall or waves breaking against shore.
Plants and animals release organic compounds as they decompose, and these compounds lessen the surface tension of water and create bubbles. Biodegradable detergents and reduction of pollution from wastewater treatment plants have reduced the occurrence of pollution-related foam.
If the foam smells fragrant or perfume, it may be from a nearby spill or waste discharge pipe. Natural foam may smell fishy or earthy, and may be white, off-white, or brownish, and breaks apart easily when disturbed.
When to contact The City
If you suspect water pollution in any local waterway, or if you’re unsure about the cause of something you have observed, please report to the City of Coffs.