In the event of a blue-green algal bloom in a water supply, many of the precautions an irrigator should take are similar to those for any water user.

Some of the problems unique to an irrigator are:

  1. Irrigating crops
  2. Irrigating pastures
  3. Washing fruit and vegetables
  4. Rice growing

1. Irrigating Crops

Type of Irrigation:

Drip/overhead sprays


Clogging of pipes and nozzles

Contamination of crops due to algal toxins accumulating on the plant surface.


Use filters

Avoid water contact with fruit/vegetables. Wash contaminated crops in clean water

Type of Irrigation:



Algal toxins may collect on the soil surface when the water dries out. Toxins may wash into drainage channels/water supply. Other plants (grass etc.) may be contaminated.


Use clean water supply if possible.

2. Irrigating pastures

Dangers will be similar to those for irrigating crops.

  • Avoid irrigating pastures with contaminated water particularly prior to suspected long periods without rain or during drought.
  • Keep stock off a contaminated pasture. As the pasture cannot be washed it is important to keep stock of the pasture until the toxins have been washed away (usually by rain).

3. Washing fruit and vegetables

  • If the produce may have been contaminated with blue-green algae, wash fruit and vegetables thoroughly using a clean water supply (bore water, rain water or correctly treated water).

4. Rice Growing

Excessive algal growth (of all species, particularly the filamentous green algal species) can affect the growth of rice, especially in the early stages of growth. Most commonly a mixture of algal species will grow in the rice bays, with mostly the green algae and diatoms affecting rice growth.

  • Algal filaments can form a mat on the soil surface under the water of a flooded bay, inhibiting the growth of seedlings from germinated seeds in the soil.
  • Large numbers of algae can become quite dense in the water body and when they reach the surface of the water may form a dense scum. This scum can affect the rice in two ways:
  • 1. Rice can 'drown' - Successful aerial sowing of rice seeds relies on the seeds germinating in the soil with the roots establishing under the water and the shoot using its energy reserves from the seed to grow upwards through the water to the surface. A dense mass of algal filaments in the water body and/or on top of the water can prevent the shoot reaching the surface, and thus depriving the seedling of the important oxygen it needs to survive.
  • 2. Light screening - A dense mass of algae on the surface or in the water body can prevent adequate light reaching the developing seedlings, and thus reduce the photosynthesis needed to supply the growing rice plants with energy.

Once the rice has established and begins to form a canopy, the rice plants naturally reduce the amount of light reaching both the water surface, and also any algae which are present. This will help to slow the growth of algae present in the water.

Ways to prevent algal problems in the rice bays - these help to prevent the growth of algae in the water prior to emergence of rice seedlings.

  • Do not store water between seasons in channels or stagnant ponds.
  • Check for algae in the water used in the first fill of a rice bay.
  • Reduce the time between the fill and seedling emergence by pre-seeding, or aerial sowing.

For further information about how to deal with algal problems in the rice bays contact your local District Agronomist.


•  Water treatment

•  Farm dams

•  Contacts

•  What to do in the event of a blue-green algal bloom .

•  Common Questions

•  Algal Alerts

•  Algal Blooms

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? 2002. NSW Murray Regional Algal Coordinating Committee, MRACC. Unless otherwise specified, maps and images are copyrighted to Department of Land and Water Conservation, NSW.