Pasture ponds, horses and algae. Oh my!
Protect your livestock from potential illness carried in pasture ponds. Protect pasture ponds from erosion and contamination caused by livestock.
At Michigan State University Extension, educators get a lot of questions. We love questions because they offer opportunities to educate people that are eager to learn the answer. Questions can also serve to alert us to current issues and trends. A large part of our job is to be available to answer your questions. A question I was recently asked was about a pond used by a landowner’s horses. They were allowing their horses the freedom to enter the pond to forage, drink and swim. The homeowner reported that they recently noticed that their pond is green with algae and the frogs are not present this year. They were curious what could be done to remove the algae without using chemicals. Could I provide information about getting rid of the algae? Immediately, I realized that the story was more important than the question and it became a perfect extension education opportunity. The presence of excess algae is the symptom, not the problem, but for the sake of argument, I begin with that.
Algal blooms are a natural seasonal response from spring turnover releasing extra nutrients from the bottom of the pond into the water. This is normal and often calms down after the other pond plants become more active. If it does clear up not by mid-summer, then you have a larger problem with excess nutrients in your pond. Using a pond dye can help with algae control by reducing the amount of sunlight available to the algae. Using floating plastic shade cloths and moving them in the pond can also help. However, if the pond is being fertilized constantly from the horses, these measures will not help. Action needs to be taken though because late summer algal blooms can be harmful to animals drinking from ponds.
The winter pond
Typical pasture ponds are often vernal wetlands that develop into ponds seasonally and are quite small and shallow. If the top of the pond completely freezes over during the winter, there is reduced gas exchange and very low dissolved oxygen in the water. These symptoms are common and can cause turtles and frogs to die during the winter, but frogs frequently recover their populations quickly. Keeping a hole in the ice during the winter can promote gas exchange and prevent this winter die-off. Excess nutrients also use up the oxygen in the water.
The plants and fish
Adding more aquatic plants can also help by taking up the extra nutrients. It is never recommended to stock a natural pond with non-native plants and fish, especially if it is connected to a stream or larger wetland. During a heavy rain event, these non-natives can escape into the environment. If you select native plants and fish, they are already adapted to your environment and can prevent a buildup of gas under the ice. To stock fish in a pond, the water should be at least 15 feet deep or it is required to add an aerator or fountain to mix the water and to maintain oxygen levels. However, if your pond is nutrient loaded too many plants may already be an issue.
Horses and livestock need water, but if they are allowed direct access to open water, this almost always leads to water pollution problems. They contribute to excess nutrient loading from stamping in extra soil and defecating in the water and ultimately into any nearby wetlands or stream. The runoff from the pasture that enters the pond will be contaminated and will contain manure, urine, pesticides or herbicides, and dirt (sedimentation). We strongly discourage that practice. Open ponds attract lots of wildlife and can be a source of disease transmission. Water degradation from stirring the bottom and trampling the edges can also cause excessive erosion.
Reduce nutrient loading problems by fencing out direct access to the pond. You can create a stable platform so that they may drink, but not enter the pond. Another option is to pump water into a separate watering station away from the fenced off pond to protect its edges from erosion caused by sharp hooves.
Ponds for livestock should be constructed so that there is little runoff and watering tanks should be placed downhill from the pond to prevent manure from draining back into the pond. Ultimately, you must decide between managing your pasture pond as a watering hole for your horses or a natural pond for personal enjoyment. Then, plan to manage it accordingly.
The bottom line
Nutrients in the water feed algae growth. The best way to control algae without chemicals is to manage and reduce nutrient loading.
Here are some webpages that offer more information:
One Horse or a Hundred: Manure and Water Don’t Mix