Cleaner Farm Dams Workshop February 25, 2023, RALF, G&DBLG, BMRG GLM Officer, G&DLCG


A two-part hybrid Regional Agriculture Landcare Facilitator (RALF) presentation on Cleaner Farm Dams was delivered in late February 2023, onsite at the Gympie Landcare Nursery. It was developed and delivered to over 30 stakeholders with the collaboration of the Gympie and District Beef Liaison Group, BMRG’s Grazing Land Management Officer, and the Gympie and District Landcare Group. This workshop was especially important in preventing outbreaks of blue-green algal blooms, which are commonly found in freshwater systems. They occur worldwide, but drought conditions can exacerbate conditions favouring algal blooms, something to be acutely aware of coming into an El Nino weather cycle. Algal blooms also pose a significant threat to livestock if consumed or if affected water is drunk. There were therefore important points in this workshop for participating landholders to take away.

The key presenters were Dr. Martino Malerba of Blue Carbon Labs, Deakin University, and Associate Professor Larelle Fabbro, from Central Queensland University (CQU) in Rockhampton.

Topics covered included:

  • Improving water quality, carbon cycling, water security and biodiversity.
  • Basic water quality and biodiversity issues associated with farm dams.
  • Signs of problems developing in farm dams.
  • Common cyanobacteria & their toxins. Impacts on livestock health/wellbeing and feed conversion.
  • What can be done relatively cheaply to see benefits?
  • The benefits of improving farm dam management for greenhouse gas production.
  • Current policies and outlook for financial incentives associated with farm dam management.
  • Methane reduction & current initiatives for farmers and landowners. Opportunities for the future.
  • How to be a part of an upcoming study in northern Australian farm dams.



Here is the link to Part 1 of Dr. Malerba’s presentation:


Associate Professor Larelle Fabbro, from Central Queensland University (CQU) in Rockhampton was onsite to answer questions, deliver her presentation on farm dams, cyanobacteria and livestock impacts. She also led a field water testing exercise on site for attendees.

An example of a dam with very good water quality courtesy of Assoc. Prof. Larelle Fabbro, controlled by the Livingstone Shire Council.

Key points from Associate Professor Larelle Fabbro’s presentation included how livestock have been excluded, that there has not been a lot of development within the dam itself, and what goes into a dam has a huge influence on sustainable water quality.

Algal Blooms

The dam has different depths: a shallow area and bubbler for oxygenation. Higher oxygen levels and distribution generally improve water quality. It’s surrounded by different trees and plants, and there’s a huge biodiversity of life around the dam. This is not only a good sign of a balanced system, but a contributor to that balance. Note that some eucalypts and casuarinas produce large amounts of chemicals in their leaves that inhibit the growth of some types of toxic algae. They can tip the balance of life in favour of green algae and away from toxin-producing cyanobacteria, which causes blue-green algae. It’s important to note that not all blue-green algal blooms are toxic, and some blooms of toxin producing cyanobacteria do not produce visible scum, or bad smells and tastes. Cattle are more likely to drink from these. Those that are toxic may change their toxicity slowly over a period of weeks to months.

Temperature and oxygen distribution are key factors affecting algal blooms along with the level of food for cyanobacteria. To reduce the incidence of algal blooms, it is essential to minimize nitrogen and phosphorus pollution, reduce inputs of detergent and fertilizer, and limit nutrient levels in waterways. This includes the amount of rotting vegetation, for example from hyacinth that has fallen to the dam floor and is decomposing.

During warmer months, dams stratify into stable layers of different temperature. Warmer water stays on top and doesn’t mix with that at the bottom. This leads to anoxic conditions on the bottom that suit methane producing bacteria, and blue green algae thriving in the warmer top layers under high nutrient loads.

In winter, cooler nights and relatively warmer days encourage water to mix through the entire water column. This oxygenates the water and disrupts the anaerobic processes at the bottom.

With nothing to induce mixing, colder bottom strata with low dissolved oxygen levels and enough organic material, first produce ammonia, then hydrogen sulphide, and finally, after a long time, methane. Furthermore, once the dead organic matter sinks to the bottom of the dam, there is dramatically increased potential for deoxygenation and water quality deterioration.

A key to reducing the potential for these circumstances to develop is limiting the amount of organic material at the bottom of the dam.

How to assess blooms and other issues

When assessing a farm dam, look at its appearance. Cyanobacteria producing algal blooms can cause discoloured water, formation of scums, unpleasant tastes or odours, and serious reduction in water quality.

Generally, a black and smelly dam indicates decomposing organic matter in an anoxic state i.e. no oxygen. Very green dams have high algal loads, some of which can be toxic, while very white dams have a very high level of bacteria.

Blue-green algal blooms may persist for several weeks, depending mainly on the weather or flow conditions. Cooler, windy weather or increased flow may reduce or prevent blooms from occurring. Bubbling inflows of water may also disrupt the production of blooms.

Please note it is not recommended to treat blooms with algicides or herbicides as they destroy the cyanobacterial cells, leading to a rapid release of toxins into the water. Algaeicides can also adversely affect fish, invertebrates, and aquatic plants.

As the bloom dies, if the bloom contains species that produce toxins, these will be released into the surrounding water as the cells decompose. Once released, some toxins may persist for more than three months before sunlight and the natural population of bacteria in the water degrade them.

Threats posed to livestock and other animals

If poisoning occurs by ingesting the blooms or affected water, animals may exhibit a variety of symptoms including muscle weakness, lethargy, reduced or no feeding, mental derangement, diarrhea and in serious cases distress, muscle tremors and coma upon which death follows within a few hours to a few days.

Known specific neurotoxins from this region include:

  • Saxitoxins – that can cause tingling around extremities, mouth and lips, dizziness, weakness, thirst, tachycardia, paralysis and death. There is also evidence of bioaccumulation in shellfish etc.
  • Anatoxins – are neurotoxic and can present with nicotinic signs (muscle stimulation, tremors, seizures, respiratory paralysis and death.

Highly likely:

  • β-Methylamino-L-alanine, or BMAA, is a non-proteinogenic amino acid produced by cyanobacteria. BMAA is a neurotoxin and its potential role in various neurodegenerative disorders.

What should you do?

According to the Queensland Government’s DAF website, the following steps should be taken to assess the risk of animal poisoning:

  • Establish that animals are drinking the water or eating dried algae mats from the area where a bloom has been identified.
  • Have a suitably qualified laboratory examine a sample of the water from the dam. They can identify the cyanobacteria in the bloom and determine whether they are present in numbers large enough to constitute a risk.
  • Care should be taken to avoid direct contact with scums or suspect water while taking samples. Wear rubber gloves if taking samples and wash thoroughly with clean water following exposure.
  • If necessary, the laboratory may advise you that it would be appropriate to identify and measure the toxins in the water.

2023 Cleaner Farm Dams V2