Algae & blue-green algae

concentration of chlorophyll-a in water at monitoring points (freshwater, estuarine and marine)
cell numbers of total and blue-green algae in water at monitoring points (freshwater, estuarine and marine)
number of days of closure of lakes, rivers and/or beaches to recreational use due to blue-green algae

Indicator description

Algae are the simplest form of plant life. A count of all the algae present (as measured by chlorophyll-a levels) is used to indicate the productivity of aquatic systems. In conditions of warm, poorly mixed, nutrient rich waters, algal counts may grow to extremely high densities.

These conditions can occur when streamflows are very low, due to low rainfall or over-consumption of water, or due to high levels of sediments and nutrient being added to the stream system.

Under these conditions, the likelihood of high counts of blue-green algae (cyanobacteria) occurring is increased. Blue-green algae are not true algae, but they are aquatic organisms which have some properties that are characteristic of bacteria and some that are characteristic of algae. High counts of blue-green algae may potentially render the water unsuitable for human use because some species produce chemicals that can be toxic to humans and livestock.

The amounts of algae and blue-green algae are of interest to State of the Environment reporting because these reflect the impact of human activity and other environmental factors on the aquatic environment, and also the suitability of water for continued use by humans and other species.