Dugouts are a great source of water for cattle on pasture. In many cases, they provide water to pastures that would otherwise be unusable in the summer. However, concerns may arise about what is growing in the dugouts – specifically, if a growth will be harmful to cattle. It is crucial to identify what is present so that proper action can be taken if needed.
Duckweed
Duckweed is commonly mistaken as a blue-green algae bloom. It is actually a free-floating plant whose leaves help it sit on the surface of the water. It can be easily identified by its bright green colour and hair like root that descends below the surface of the water. The root can be clearly seen once the plant is removed from the water. Duckweed's disc-like leaves could be described as miniature lily pads.
Duckweed is not harmful to cattle and is actually considered beneficial for a dugout. These tiny plants form a thin mat on the surface of the water that prevents light penetration into the water column. At the same time, the roots are drawing nutrients out of the dugout. Both of these functions help to reduce algae and cyanobacteria growth.
If duckweed is present in your dugout, no action needs to be taken.
Green Algae
Green algae is also quite common in Saskatchewan. Our climatic conditions and the nature of our dugouts provide the right combination of nutrients, light, water and temperature for algae to thrive. It also commonly develops in stock tanks and water bowls. Green algae can be identified by scooping some of the bloom out of the water; be sure to wear a rubber glove when doing this. If it is filamentous, like a matt of tangled wet hair, and a deeper green than duckweed, it is probably algae. Although green algae is not typically a problem for cattle, it can be a nuisance for water delivery systems.
It is not uncommon to have algae clog intake lines and filters. To prevent clogging, it is best to have intakes located in the centre of the dugout approximately three to four feet below the surface of the water.
Cyanobacteria – Blue-Green Algae
Cyanobacteria is free-floating and usually distributed in the top three feet of the water column. Unlike green algae, it will be difficult to pick up out of the water and its appearance can range from looking like a paint spill to grass clippings with a colour that may be green or blueish-green. Some strains of cyanobacteria are potentially dangerous; in the right conditions some will produce deadly toxins that act on the nervous system and/or the liver.
Cyanobacteria grows rapidly, appearing almost overnight – this is called a bloom. The deadly toxins can also be produced very quickly. When there is a disturbance to the water body causing the bacteria stress, the toxins will be produced and released. Toxin release most commonly occurs because of a wind event that mixes and disturbs the water, causing the cyanobacteria to die and release the toxins. In the case of a wind event, often the cyanobacteria and toxins will be pushed to one end of the water body where the deadly toxin will be further concentrated. When this happens, there is a serious risk to animals that are directly accessing the water and drinking along the shore. Livestock should be prevented from drinking from that water body for 14 days after a bloom occurs to prevent death losses.
If cyanobacteria needs to be treated in a dugout then the recommended treatment option is a registered copper sulfate product. It is important to remember that if you decide to treat the water it will kill the cyanobacteria and cause toxin release. Again, livestock must be removed from the water for 14 days; therefore, you must have an alternative water source available. It is also very important to correctly calculate the volume of water present to avoid overtreatment with product. When treating a dugout, it is not recommended to exceed three treatments in one season.
There are a couple of things you can do to prevent or limit algae and bacteria growth in livestock water sources. Restrict or remove direct livestock access to the water by setting up a remote watering system. This will increase vegetation around the water body, which will, in turn, naturally filter nutrients out of runoff water. It will also reduce or eliminate nutrients directly deposited from livestock manure and urine. Funding for projects such as this may be available through the Resilient Agricultural Landscapes Program and the Farm and Ranch Water Infrastructure Program. Aeration of the dugout or slough is another option that will help to limit algae and bacteria growth and will promote a healthy aquatic ecosystem.