​​​​​​​Algae are a diverse group of organisms that are widespread throughout aquatic habitats, both fresh water and marine. They range in complexity from single celled to multicellular organisms such as large kelps that can grow to over 50 metres in length. There are two basic groupings of algae being microalgae (phytoplankton) which are visible usually only with the aid of a microscope and macroalgae (commonly called seaweed) that can be seen with the unaided human eye.


Microalgae (most phytoplankton), are single celled photosynthetic organisms that are only visible with the aid of a microscope. Microalgae vary in size from a few micrometres (1/10,000th of a centimetre) to several hundred micrometres. They can exist as individuals or form chains or groups. Microalgae thrive in a wide range of habitats including fresh and salt water, blackish, marine and even soil environments. Unlike higher plants, microalgae do not have roots, stems, or leaves. Profuse growth of microalgae results in algae blooms. In some instances, blooms may have a negative effect on the environment, and are termed Harmful Algal Blooms (HABs).


Macroalgae, or sea weed, are multicellular algae that are generally visible to the naked eye. Typically they are attached via a holdfast to substrate, such as rocks, submerged structures (e.g. pylons) or other plants (e.g. seagrass). Some species are free-floating and drift with the water currents. Macroalgae are a natural component of an aquatic ecosystem and play a role in cycling nutrients and are also important habitat and or source of food for invertebrates, fish, mammals and birds.

Algal Gr​​​owth

Algal growth is dependent on light availability, water temperature and, nutrient availability. For temperate zones, such as Tasmania, low light levels and low water temperatures limit the growth of algae during the winter months. During spring as the amount of available light increases and water temperature rises, conditions are more favourable for macroalgae growth. During summer growth rates for some species may slow when water temperature exceeds the optimal temperature range.

The transport of macroalgae, seagrass and other organic matter by prevailing weather conditions and water currents may result in the accumulation of material on the foreshore. Such accumulations are known as wracks and are a natural component of coastal ecosystems. The wrack material contributes to the food web dynamics and nutrient cycling of foreshore, coastal and marine communities.

Issues relating to algae

Should you have concerns relating to nuisance algae in your area, and,

If urgent

Contact the EPA Incident Response Hotline 1800 005 171, or email to

Or if non urgent

Email to