Algal data

What is algae?

Algae refer to a diverse range of photosynthetic organisms living in freshwater. They are also called phytoplankton (from Greek 'phyton' means plant and 'planktos' means wandere). These organisms could be either single cell or multi-cellular and photosynthetic.

Most algae in freshwater systems are harmless. However, some algae (i.e., some blue-green algae species) produce toxins that are harmful to humans and animals if ingested through drinking water or come into contact with polluted water. Most of these organisms are microscopic, which means you cannot see them to unaided eyes. However, when they grow into large colonies (often called 'algal blooms'), they can be visible as green spots in water or sometime they make surface scums. Algae like living in nutrient rich, warm (250C), low turbid, stable water.

Algae monitoring in the Hawkesbury-Nepean River

The types of algal species often vary with different seasons of the year and over different locations. NSW Office of Water and Regional Algal Coordinating Committee monitor the river system at key locations and release timely alerts for river users if any toxic blooms are present. To learn more about algal monitoring in the river system, please visit NSW Department of Primary Industries (opens in a new window).

The algae problem in the river system has been an ongoing issue viz., large algal blooms reported in 1983, 1985, 1988 and 1991 (Hawkins et al., 1994, Saunders and White, 1993). However, the intensity (i.e., distribution) and the frequency of blooms have reduced over the last 5-10 years. The prime reason for phytoplankton blooms in the river system is the presence of plant nutrients in excessive levels. These nutrients are added to the river system mainly through diffuse-source pollution from urban and agricultural runoff (during high flow periods) and treated effluent from STPs (during low flow periods) (Bishop et al., 2002, Krogh et al., 2008). The reduction in intensity and frequency of large algal blooms may be as a result of nutrient reduction strategies undertaken at STPs and catchment. The current algal guideline for freshwater is based on a toxic species called Microcystis aeruginosa. Depending on its concentration, the Algal coordinating committees release algal alerts notifying river users. If you are a community group interested in sampling algae as an indication of river health, the Royal Australian Botanic Gardens (opens in a new window) has some useful information on collection and identification of algae in Australia.

The following table consists of guideline values related to algal alert system used in NSW. This system is based on number of cells per milliliter or cell bio-volumes of freshwater cyanobacteria (Microcystis aeruginosa) that produces neurotoxins and hepatotoxins.

Alert levelGuideline
  • When >50,000 cells of Microcystis aeruginosa are present or a biovolume of all toxin producing cyanobacteria exceeds 4 mm3/L or,
  • when the total cyanobacteria (toxic and non- toxic) exceeds 10 mm3/L or,
  • when scums are present for long periods.
  • When cells of Microcystis aeruginosa concentrations are between 5000 and 50,000 cells/mL or,
  • when the bio-volume of all cyanobacteria is between 0.4 and 4 mm3/L.
  • When Microcystis aeruginosa 500 cells/mL of or total cyanobacterial biovolume >0.04 mm3/L, but below the Amber alert level

Source : Department of Primary Industries, NSW Office of Water

Algae trends at Penrith, Cattai, Sackville and Lower Portland

Please use below links to access weekly algae levels (toxic and potential toxic species) at Penrith, Cattai, Sackville and Lower Portland. We will be progressively updating this space as more data become available.

Toxic species from 4 November 2013 to 17 February 2014 () PDF, 85.93 KB (opens in a new window)

Potential-Toxic species from 4 November 2013 to 17 February 2014 () PDF, 86.42 KB (opens in a new window)

Want to know more about algae and toxins ?

Here are some interesting reading resources.

Blue-green algae (cyanobacteria) and water quality (opens in a new window)

Algal blooms: A colourful danger (opens in a new window)


BISHOP, K., GROWNS, I., CHURCH, T., WARNER, R. & TAYLOR, E. 2002. Status of the Health of the Hawkesbury Nepean River. Independent Expert Panel On Environmental Flows , For The Hawkesbury Nepean, Shoalhaven And Woronora Catchments.

HAWKINS, P., HILL, B., SAUNDERS, J., KOBAYASHI, T. & WINDER, J. 1994. Algal bloom dynamics in the Hawkesbury-Nepean River (October 1992- March 1993), West Ryde, NSW, Australian Water Technologies.

KROGH, M., WRIGHT, A. & MILLER, J. 2008. Hawkesbury Nepean River Environmental Monitoring Program: Final Technical Report [Online]. Sydney: Department of Environment and Climate Change NSW and Sydney Catchment Authority.

SAUNDERS, J. & WHITE, B. 1993. The blue-green algal bloom in the Hawkesbury River at the Sackville Ferry during the summer of 1991/2. Wetlands (Australia), 12, 30-38.