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Removing/preventing green scum on surface of pond

Removing/preventing green scum on surface of pond


Old 06-12-06, 07:04 AM
Thread Starter
Join Date: Jun 2006
Posts: 3
Removing/preventing green scum on surface of pond

Good morning everyone.

Some advice please.

A few years ago, I purchased a "week end" place in South Eastern Wisconsin that has a 200 foot by 100 foot pond on it.

I believe that the water inside the pond comes from snow melt and rain.

This pond is about 3 feet deep.

The pond, is in a very "wooded" area and gets very little direct sun light. (Except for an hour or so at noon when the sun is directly overhead.

My guess is that this pond has been in the current state for 100 years or more.
This is a very rural area and has NEVER been developed.

In fall, when the water lever is way low, I have been able to walk out into the pond 10 feet or so.
For grins, I tried digging down some to see what I might see.
I was able to get down about 2 feet in spots and found solid leaves.

In spring, it is filled with frogs and such.
And all summer long, ducks and deer stop by.

Here's the deal.
The pond always gets this green algae like stuff over the surface.

I'm seeking advice on how to deal with it.

Is there a way to eliminate it ?

Is there a way to scrape it off the surface ?

Would adding an aerator help ?

Would swimming pool chemicals be appropriate ?

Any suggestions or ideas would be greatly appreciated.

Thanks in advance.

Ray in Wisconsin
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Old 06-12-06, 07:51 PM
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Join Date: Mar 2003
Location: NC, USA
Posts: 18,591
Is it algae or something else? Are there visible leaves or roots? Is it a green "slime" or hair like mass?
Old 06-13-06, 06:11 AM
Thread Starter
Join Date: Jun 2006
Posts: 3
Happy Tuesday morning.

Thanks for the reply.

Good questions.

I'm not really sure if it IS Algea or not.

There aren't any roots or leaves, that's for sure.

This stuff floats on the surface of the water.

The coclor is very light green.

I have used a rake to pull some of the stuff on to the grass next to the pond.

When I look at the mass as it lays on the grass, it appears as if it is made up of tiny little multi sided, (kind of star shaped but with more point, if that makes sense) individual "things".

And this stuff smells. That's for sure.

It's kind of hard to describe.

And it's got to be even harder for you, to understand what I'm decribing.

Methinks, I need to do some work to identify what this stuff is.

Ray in Wisconson
Old 06-13-06, 10:56 AM
Join Date: May 2006
Location: Bremerton
Posts: 42
Questionable scum?

So from what I have read this is a natural pond? Algea is a product of ponds, you can add chemicals but you need to be careful, some chemicals will hurt the wild life. They do have some chemicals.

Do you have power near the pond ? Airation always helps. they even have solar pumps now. If you can get some water movement it will help.

Does the pond have water in it year round ? If so you can look into critters that eat algea ....
Old 06-13-06, 12:15 PM
Join Date: Aug 2000
Location: USA
Posts: 15,834
Keeping pond water in motion helps oxygenate the water, leech out contaminants, and prevents stagnation that becomes a medium on which algae and insect larvae to feed. Perhaps a solar powered waterfall or fountain would provide necessary movement.
Old 06-13-06, 06:58 PM
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Join Date: Mar 2003
Location: NC, USA
Posts: 18,591
Generally the root cause of pond problems is too many nutrients. You can oxygenate to encourage aerobic bacteria to break down nutrients. You can mechanically remove nutrients. You can trim tree around the pond to reduce the amount of leaves (nutrients) from falling into the pond. You can also chemically kill the stuff you don't like which does not fix the root problem so the green growth will likely return.

I consider solar fountains ornamental only and without significant benefit unless your budget has a coma in the price. Granted any water movement and/or aeration will be beneficial but there is just not much power available from inexpensive solar fountains and aerators. With your 1/2 acre pond you need to think industrial size. Also, the algae and other plants in the pond produce oxygen during the day when the sun is shinning and at night they go into reverse and consume oxygen from the water. A solar powered anything does its' work when it is needed least and stops working when it is needed most (at night).

Mechanical harvesting will help. Make sure you discard the waste far enough from the pond that the nutrients do not get washed back into the pond. Be prepared for a Herculean task. There are billions of plants in your pond all growing and reproducing and there is only one of you. You can make some great compost if you do it properly.


I am going through a similar situation with a 1 acre + pond here in NC. Everyone I consulted said that draining the pond and digging out the muck was the quickest and easiest way to go. If not draining & digging they recommended 1hp of aeration per acre running 24/7. They also recommended about $1'000 of chemicals. All their options were either too destructive, too expensive or consumed too much power for my liking.

I came up with my own long term plan. I figure that it will take about 5 years to START to see any lasting improvement. I have removed some of the trees around the pond. I mechanically remove about 4'000 pounds of duckweed every week during the summer and the pond is still totally covered. I also have a 1/4hp rotary vane air pump powering an aerator about 8ft deep running for 12 hrs during the night. I have stocked the pond with various plant eating fish. Where the creek flows into the pond I have built a bamboo, cattail & grass "marsh" to filter the water entering the pond. With all of this I figure my 5 year plan has a 50/50 chance of succeeding.

Check back in 4 years and I'll tell you if my plan worked.
Old 05-03-12, 01:02 PM
Join Date: May 2012
Posts: 1

It has been over 4 years. How did the plan turn out?
Old 05-03-12, 02:03 PM
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Join Date: Mar 2003
Location: NC, USA
Posts: 18,591
The plan worked out extremely well. While a pond in the south will never be crystal clear it is as ideal as it can get. I no longer have to expend much effort. There is no stagnant pond smell, there are no floating weeds and no choking algae blooms. The koi and white amur have grown huge and keep the weeds at the water's edge well trimmed and they are big enough that the herons are no longer a concern.

The one failure has been my marsh area. The koi are such voracious eaters they have decimated the cattails and other plants. I have a small "wetland" area remaining and I think I've stabilized it by driving bamboo stakes in the perimeter as a fence to block the fish but low enough for the turtles and frogs to cross.

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