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Department of Primary Industries:
Blue-Green Algae In Farm Dams

Recently, blue-green algal blooms have been confirmed in several locations in Gippsland.

By Department of Primary Industries - 9th April 2003 - Back to News

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Recently, blue-green algal blooms have been confirmed in several locations in Gippsland. Blooms have been detected in the old course of the Tambo river system at Tambo Upper, but of greater concern to many farmers should be the presence of potentially toxic blue-green algae cells in farm dams. Livestock losses from blue-green algal blooms are rare, but the presence of any significant level of contamination brings a potential risk.

Algae are single cell organisms that can live independently, or which may group together in colonies. Blue-green algae are a poisonous form of algae, often colonising to form a scum over the surface of a body of water. In low numbers, blue-green algae are rarely a cause for concern. However, a bloom can multiply in size in a short period of time, increasing algal concentrations in water and the potential for harm.

Blue-green algae occur naturally in waterways. Once suitable conditions for growth occur, algae will multiply. Favourable conditions include high levels of phosphorus, warm, sunny days, warm water and calm conditions. Elevated water temperatures are a consistent factor during summer and autumn, and are compounded by the current low water levels in many farm dams. Blooms may occur in winter months too, if each of these conditions is met.

Livestock and other animals having access to water colonised by blue-green algae are at risk of poisoning. Harmful toxins are released into water following the death of blue-green algae cells. Poisoning results from ingestion of these toxins, which are very stable and can persist in water for weeks after the algae have disintegrated. Similarly, ingested algal cells can also release toxins once they have been broken down in the gut environment. Affects of poisoning may be damage to the liver through to death, usually within a few days. Common signs include muscle tremors, staggering and convulsions. Affected animals that recover may experience chronic liver damage and photosensitization. Dairy cows may show a production decline. There is no cure for affected stock.

The risk of blue-green algal blooms can be reduced by limiting the accumulation of agricultural waste and nutrient run-off into farm dams and in waterways. Opportunistic clearing dams of sedimentation is another option. Livestock can remain on an area to graze, but access to affected water should be prohibited until the risk has abated.

Under suitable environmental conditions that support blooms, farm dams should be checked daily. If a bloom is detected immediately provide livestock with an alternate water source, and exclude access to the affected dam. A solution may be to siphon water from a deeper segment of the dam into a stock trough. Ultimately, long-term exclusion of livestock from the dam can assist to limit the accumulation of organic material.


Successful seed potato exports initially depend on growing the crop for that purpose and avoiding the temptation to export "leftovers". Once the crop is grown, good handling practices are the primary concern. Loading seed that is damaged or open to infection is inviting a low-quality outturn at the destination, which can be costly in terms of time, money and business reputation.

Harvesting early enough for the product to be correctly prepared is a crucial part of planning the export shipment. Some of the critical steps in preparing seed potatoes for export are:


Do not harvest if the soil is extremely dry or extremely wet.

Drop heights should be minimised, to prevent cuts and bruises.


Harvested seed should be stored in a well-ventilated shed, with spaces between rows of bins.

Make sure that seed is dry prior to grading; if it is wet, use drying fans in the shed.

Harvested seed should be kept at least 5-10 days in the shed to dry and cure before grading.


Make sure that the tuber temperature is above 10C.

Check that the grader is clean.

Minimise all drops of the seed in the grading line and provide padding.


The aim of curing is to enable tubers to rapidly form a new skin to cover wounds. Freshly graded seed should not be loaded into containers.

Ideally, seed should be cured in the shed at 14-16C and 85-95% relative humidity, with good airflow, for 10-14 days.

The curing period may be reduced to 5-10 days by raising the temperature in the centre of the stack to 15-20C.


Handle bags gently while loading the container.

Leave a gap above the bags for air circulation.

Make sure the air inlet in the container is opened.

General shed hygiene

High-pressure wash and disinfect the grading shed, grader and bins regularly during the season.

Regularly dispose of all potato waste and soil from in and around the shed.

Use a footbath at the entrance to the shed.

Poor quality exports reflect badly on the industry as a whole. Taking full advantage of potato export opportunities will only be possible if there is a strong commitment to landing high-quality product in overseas markets.


The National Livestock Identification Scheme (NLIS) is in its second year and this year new requirements are in place as the scheme heads towards full implementation in 2005.

In addition to all calves born after 1st January 2002, the 2003 requirements are:

All cattle regardless of age that are sent from a Victorian property to a store or breeder sale at a Victorian saleyard (including dairy heifers) must be identified with an electronic tag.

All cattle moving between Victorian properties in private sales or clearing sales must be identified with an electronic tag.

All cattle arriving on your property that are not already identified with an electronic tag (either purchased in Victoria or from interstate and including purchased Bobby Calves) must be identified with an orange post-breeder tag within 30 days of arrival.

Cattle moving onto your property on agistment must be identified with an electronic tag within 30 days of arrival if they are not already tagged. As each agistment circumstance varies, call your local DPI office or the DPI Tag hotline 1800 678 779 for advice.


Tailtags are still required when you sell cattle as well as the electronic tags until the scheme is fully operational.

White electronic tags (Breeder Tags) are for cattle you have bred yourself.

Orange electronic tags (Post Breeder Tags) are for cattle you have purchased from someone else.

Electronic tags should be placed in the right (offside) ear with the thick button to the front and well into the ear to avoid losses.


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