Blue-green algae

Blue-green algae are a type of bacteria known as cyanobacteria. It is a blue-green coloured micro-organism that photosynthesises to produce oxygen. Common algal species found in our waters are Trichodesmium and Lyngbya majuscule.

blue-green algae waters
Source: Adam Wardrop

Blue-green algae needs sunlight to grow and occur in rivers, lakes, and watercourses where conditions permit. It can exist in both salt and fresh water and is part of a healthy ecosystem. In normal conditions, the cyanobacteria exist in low numbers in waterways.

Blooms can be 'harmful algal blooms' or 'nuisance algal blooms'. A harmful algal bloom is one where the alga species produces toxins that pose a threat to humans, animals, and the environment. Nuisance algal blooms are not known to produce toxins.

What causes it?

Thick dense colonies called 'cyanobacteria bloom' can grow quickly under certain conditions. These include:

  • an increase in nutrient levels (for example, nitrogen and phosphorous)
  • high sunlight
  • warm water temperatures
  • stagnant and drought conditions.

Health risks & impact

Cyanobacteria generally lives near the water's surface. It accumulates in certain areas of waterways. This is due to wind and currents, which can cause cyanobacteria to clump near the water's edge.

Cyanobacteria algal bloom
Source: Adam Wardrop

In some cases, cyanobacteria use the sunlight, nutrients and dissolved oxygen to bloom excessively. These blooms can be toxic and have a detrimental impact upon aquatic ecosystems. Cyanobacteria blooms also discolour the water and create a smelly scum on the surface near the shoreline.

As the toxins from blue-green algae are a health risk, if it is in a waterway you should refrain from:

  • activities that result in contact with that water, including swimming
  • consuming seafood obtained from the water, including shellfish, oysters, mussels, crabs, and fish
  • allowing pets to enter the water.

If you have any health symptoms after contact with infected water or eating fish from a waterway with cyanobacteria bloom, please see your doctor or call 13 HEALTH (13 43 25 84).

Preventing blue-green algae blooms

We monitor cyanobacteria levels in accordance with National Guidelines and provide advice to the public and government bodies when elevated levels are identified in a waterway.

We can prevent blooms by limiting the amount of nutrients that enter the water. Detergents and fertilisers have a high concentration of nitrogen and phosphorus, which encourage blue-green algae to grow. Being mindful about the levels of these in the detergents and fertilisers you use can reduce the blooms.

The proper disposal and use of fertilisers will limit nutrient levels in waterways. Washing your car on the lawn rather than the road or driveway can minimise the levels spilling into local waterways.

Reducing sediment runoff and soil washing into the waterway can reduce cyanobacteria blooms. Learning more about sediment control on building sites.

Report this problem

If you notice cyanobacteria bloom in our waterways, please contact us by:

Report water pollution

Trichodesmium species

This is commonly known as sea sawdust, whale food and sea scum. It naturally appears in tropical and subtropical ocean waters. Trichodesmium is a member of the phytoplankton family. It plays an important role in the aquatic food chain.

Source: Adam Wardrop

The blooms are most common between August and December. You may have noticed it washed up on a beach, in an estuary area or in the Broadwater. It can cause water to appear rust coloured, with traces of grey, green and purple streaks. There may also be an unpleasant 'fishy' smell. In stagnant conditions, blooms can release a clear toxin that changes the blooms' colour from rust brown to green. It also releases a pigment that colours the water pink.

Usually, Trichodesmium is barely visible, but in water that has been calm for long periods it begins to float like sawdust. The algal cells can join up to each other in strings and clumps. As the cells age, they become buoyant and rise to the surface. During calm conditions these cells can cluster into huge slicks that are sometimes so vast they are visible from space. Northerly currents and warm water temperatures can cause large clusters to occur.

It is recommended that you do not swim or wade in areas where the bloom is visible in the water. Also avoid direct contact with material washed up onto the beach. The concentration of the toxin in a natural system like the ocean is generally not high enough to be harmful to human health but it does have the potential to cause skin irritation. If you come into contact with it, wash with soap and clean water as soon as possible. If symptoms continue please see your doctor or call 13 HEALTH (13 43 25 84).

Lyngbya species

Lyngbya (Lyngbya majuscule) is commonly referred to as 'mermaids hair' or 'fireweed'. It is an unbranched threadlike cyanobacteria, often found in tropical and subtropical coastal environments. It is found in sheltered estuaries and bays, commonly within seagrass communities.

Lyngbya can grow 30 metres below the water surface while attached to rocks, sand or seagrass. Rough seas can disturb the bottom-growing lyngbya, creating large floating mats on the water surface. These floating mats drift with the currents, winds, and tides. They are then stranded on beaches and foreshores.

Blooms can occur at any time of the year. They are most common in south-east Queensland between the October and March. In recent years, blooms appear to be increasing in frequency and size in our region. Climate change may influence their frequency or geographical distribution.

Lyngbya can rapidly occur under the right conditions, including:

  • an increase in nutrients in water such as nitrogen and phosphorus
  • warm water temperatures
  • high sunlight.

Blooms can impact environmental and human health. It can smother seagrass, coral, and other aquatic habitats. It contains chemicals that can cause skin, eye and respiratory irritation for humans.

Some Moreton Bay fishermen experienced dermatitis and asthma-like symptoms after coming into contact with cyanobacteria. Please see your local doctor or call 13 HEALTH (13 43 25 84) if you experience any of these symptoms after coming into contact with lyngbya, or eating fish/other marine species from the waterway.

To avoid being affected by lyngbya, refrain from:

  • swimming and wading in areas where lyngbya are growing or floating in the water
  • consuming seafood obtained from the waterway including shellfish, oysters, mussels, crabs and fish
  • touching material washed onto the beach or water's edge
  • allowing pets to enter the water.

We monitor cyanobacteria levels in accordance with National Guidelines and will provide advice to the public or government departments should elevated levels be identified.