Tackling Common Dam Problems – Odours, Overgrown Vegetation, and Oily Sheens

Q. We have a dam that is about 20 years old. The last couple of years it has started to smell, it is now unbearable. I would like to know what product to use to fix this. It also has Lilys and reeds on it. Are these classed as weeds? Second dam has less weeds but an oil slick like substance on top.

ANSWER

Dams are valuable assets, providing water for irrigation, livestock, and even recreation. However, they can also be prone to issues like unpleasant odours, excessive weed growth, and unsightly surface sheens. Fortunately, these problems are often manageable with the right knowledge and tools.

Banishing Bad Smells with Beneficial Bacteria

That foul odour emanating from your dam is usually a sign of excess decaying organic matter. This build-up happens when there isn’t enough dissolved oxygen to efficiently break down dead leaves, plant debris, and other organic waste. A simple solution is to introduce beneficial bacteria, often available in tablet form.

These “Muck Breaker” tablets contain bacteria that actively consume the dead organic matter, converting it into odourless gas.

Application: Typically, you’ll need 4 tablets per 1,000 square meters of dam surface area.

Initial Treatment: Distribute the tablets evenly across the dam’s surface every two weeks for the first 6-8 weeks.

Maintenance: After the initial treatment, switch to a monthly application to maintain a healthy ecosystem. If the smell returns, resume the more frequent treatment schedule.

Controlling Vigorous Reeds and Lilies

While some aquatic plants are native and beneficial, they can become problematic in nutrient-rich water, growing excessively and outcompeting other plant life. Reeds and lilies are common culprits. Before taking action, identify the type of plant and determine if it’s a native species.

If you decide to remove overgrown vegetation, you have two main options:

Manual Removal: Tools like a weed razor are effective for physically cutting and removing the plants. This method is labour-intensive but avoids the use of chemicals.

Aquatic Herbicides: For larger infestations, aquatic herbicides can be a more efficient solution. Select a herbicide specifically designed for aquatic use and follow the instructions carefully. Important: Be aware of any withholding periods, which dictate how long you must refrain from using the water after application. For example, some herbicides require a 10-day withholding period.

Addressing Oily Surface Sheens

That unsettling oil slick appearance on your dam’s surface could indicate a few different issues:

Algae Bloom: Algae, particularly certain types, can create an oily sheen. If the sheen changes colour from red to green, it could be Euglena, a type of algae. A predominantly green tint suggests blue-green algae.

Stormwater Runoff: Heavy rainfall can wash oils, fats, and other pollutants into the dam, resulting in a surface sheen.

Decomposition: The breakdown of organic matter, especially in standing water, can release oily substances that form a slick.

Here’s how to address each potential cause:

Algae Control: An algaecide like Coptrol can effectively kill algal cells. While Coptrol allows immediate water use, be mindful of the potential for deoxygenation as the algae dies, which can harm fish. Consider aeration if you have a significant fish population.

Decomposition: If the sheen is due to decomposition, the muck breaker tablets mentioned earlier can help break down the organic matter and eliminate the oily film.

By correctly identifying the problem and implementing the appropriate solution, you can maintain a healthy, clean, and aesthetically pleasing dam.

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by Aquatic Technologies
If you have any questions regarding looking after your dam or pond and what products are the most suitable for your situation, please read through the helpful articles on our site or feel free to contact our friendly team who can help you maintain proper health in your water body year round.
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