Is that a slick on your dam? Understanding and Addressing Surface Films
Q. Over the years muck has collected on the bottom. This year we have a problem with duck weed. After recent heavy rain the pond has developed a thick greyish surface slick. Not sure if it is algae or bacteria. Can you advise what we can do to clear it and the rotting vegetation on the bottom?
ANSWER
If you’ve noticed a grey or black slick forming on the surface of your dam, it’s understandable to be concerned. While it might look like algae, chances are it’s something else entirely. Unlike blue-green algae, which will always have a green or bluish tinge, these darker slicks usually point to the presence of fatty or oily substances. So, what’s causing it, and what can you do?
Common Culprits
Several factors can contribute to the formation of these surface films, particularly after heavy rainfall:
Stormwater Runoff: Heavy rain often causes stormwater overflows, which can carry a variety of pollutants into your dam. This includes oils, fats, and other debris that find their way into the water system. You’ll likely notice this type of slick concentrated near the areas where water enters the dam.
Stirred-Up Organic Matter: Heavy rain can also churn up the bottom of the dam, disturbing decaying plant matter, animal excrement, and other organic materials. While this can make the water appear cloudy and dark overall, if these materials are oily (perhaps from specific bacteria or organic decomposition), they might blend together on the surface forming a slick.
How to Deal with the Slick: A Step-by-Step Approach
The good news is, there are solutions to treat this issue. Here’s a recommended approach:
Muck Breaker Tablets: Begin by using two muck breaker tablets in your dam every two weeks for the first 6-8 weeks. These tablets are designed to work in two ways: first, they help break down organic matter at the bottom of the dam, and secondly, they introduce beneficial bacteria. These bacteria are vital for reducing excess nutrients and organic pollutants, leading to a cleaner, healthier dam.
Monitor and Locate: Keep a close watch on the grey film during those first 6-8 weeks. Try to pinpoint any specific areas where water enters the dam. This helps identify potential sources of pollution.
Filter Entry Points: If you find specific entry points where runoff is entering the dam, you can use a simple and effective filter. Stake a straw bale (ensuring it doesn’t contain any seeds) at the entry point. This will help reduce excess sediment and filter out some bacteria from the incoming water.
Ongoing Maintenance: After the initial 6-8 week period, switch to using two muck breaker tablets monthly. This will help maintain the beneficial bacteria population and continue breaking down residual organic matter, keeping your dam cleaner in the long term.
When Stagnant Water Becomes a Problem
If your dam tends to be stagnant, the lack of water movement can allow bacteria to thrive. If the problem persists even with the use of Muck Breaker tablets, consider aeration as an additional measure. Increasing its oxygen levels can significantly improve the water quality.
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