Algae in my pasture pond

Asked March 27, 2018, 12:10 PM EDT

How do I get rid of the excess algae without using chemicals? It is not an overly large pond 25 feet across and about 8 feet deep at the center. It is fed by run off from 60 acres that then feeds into a seasonal creek. Up until this year it was a very healthy pond with grasses and Lillies. I have noticed there are not as many frogs either. Will introducing gold fish and replanting water plants fix it? My horses ate most of the water grass last year so I think that may be where the problem started. Just guessing. Thanks for any help you can offer.

Polk County Oregon

1 Response

Hello and thank you for contacting eXtension with your pond algae question. I have addressed your concerns (and mine) below.

Let me begin with algae. 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 going into the pond. Floating plastic shade cloths and moving them about the pond can also help.

The size of your pond indicates that is quite small and shallow, and during rain events feeds an ephemeral stream. If the top of the pond completely freezes over during the winter that would lead to reduced gas exchange and cause very low dissolved oxygen in the water. This is common and can cause a fish and frog die off during the winter. Frogs seem to find their way back. Keeping a hole in the ice during the winter can promote gas exchange and prevent winter die-off. Excess nutrients also use up the oxygen in the water.

Replanting and stocking. Adding more aquatic plants can also help by taking up the extra nutrients. It is never recommended to stock a natural pond, especially one connected to a stream, with non-native plants and animals. During a heavy rain event these can escape into the environment. Always stock ponds with native plants and animals. They are already adapted for your environment. Additionally, because of the sized of your pond, to stock fish may require deepening your pond to 15 feet and adding an aerator or fountain to mix the water and to maintain oxygen levels.

Livestock let to freely enter ponds always leads to pollution problems. They contribute to excess nutrient loading in the water and in your case, ultimately into the stream. I strongly discourage that practice. Reduce nutrient loading problems by fencing out direct access for your horses to the pond. You can create a place so that they may drink but not enter the pond. Another option is to pump water into a separate watering trough away from the fenced off pond to protect its edges from erosion caused by sharp hooves. Ultimately, you must decide between managing your farm pond as a watering hole for your horses or a natural pond for personal enjoyment. Then, plan to manage it accordingly.

Bottom line: Nutrients in the water feed algae. The best way to control algae without chemicals is to manage and reduce nutrient loading.

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