It sounds like Fairy moss, which isn't a bad thing to have as it serves as food for birds and fish.

If you want to get rid of these surface plants, I think the best thing to do is manually scoop them out, but they multiply rapidly.

Or get lots of hungry koi!

Thankx for the reply but maybe this is not the weed I may have led you to think it is as chokes everything up and you can not see one clear patch of water looks horrible, when I had Kois in it they all died through lack of oxygen I guess, I used to try to net it but the ponds far too big would take forever, would barley straw help do you think . . .

Are you able to take a picture? If it is stringy close up and looks almost like green wool, it could be blanket weed/string algae. However, that shouldn't be killing your koi, as it actually provides oxygen for them. Maybe they died from other causes? Do you have water movement or filtration of some sort set up? You could test the water and see if there is ammonia or nitrites which would harm the fish in sufficient concentrations. High levels of phosphate and nitrates would explain the large amount of algae.

I think people have had mixed results with barley hay. You can also use a chemical algaecide. Before you spend lots of money though for such a large pond, I would test your water in a few different spots and see what that tells you.

Sorry I can't be of more help!

Is this what your "weed" looks like?
http://forums2.gardenweb.com/forums/load/ponds/msg0913300725060.html

I will try to take a photo ir 2 of it they are like tiny individual light green bits and they all join together and cover the pond ( more a lake really) when anything is thrown in they seperate then re cover the hole again in seconds like little stars almost . . . .It is not the blanket type a weed or stringy at all just these millions of little bits all joined together. ,

Could also be duckweed.

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from: http://www.nilesbio.com/prod172.html

I think barley straw is only reputed to reduce cloudiness from suspended microscopic algae ("pea soup" algae>. I use it on my full-sun lily pond and I do think it works for me. According to an article I saw on the Foster & Smith web site, the decaying straw releases a carbohydrate that causes algae (and other tiny particles) to clump together and sink. Little plants such as duck weed that float on the surface would not be inhibited by barley straw. Herbicides kill the plants but then the rotting plants return the nutrients to the water, which will in turn feed weeds or algae. I think mechanical removal would probably be a start. Other plants could be used to try to out-compete the floating plants for nutrients. If this is duckweed, ducks would love to eat it, and as was mentioned above, fish such as koi and goldfish relish it as well.

I can't keep duckweed in my lily pond because it is very effectively removed by my 2 skimmers (and possibly my goldfish). I know yours is more of a natural style pond, but perhaps you could install a pump and some sort of skimmer.

Good luck.

Sharon

Hello it is not like the photo of weed above, they are tiny star like things, there are ducks on the pond but they seem to ignore the weed and just swim through it then it separates and then close up straight away, there is no where on the pond that you can see any actual water it is just completely like a light green carpet covering the whole pond, the pond is too big to net it out at all, I will get photos and hopefully find how to put them on these pages. ( I know less about computers than I do ponds even) Pity the barley straw does not work though as that would be good if it cleared the pond . . . Reb . . .

Is adding an electric pump out of the question? I would think it would be possible to install a skimmer in the pond bank with a pump inside and run a pipe from the pump to return on the other side of the pond. Even a sump pump hose would work. This would give your pond water some movement, and as the water is drawn into the skimmer the weeds would be trapped in the basket. You'd have to clean it a lot at first, but ultimately you'd have an easy way of keeping the surface open.

Here is a link that might be useful: skimmers

Reb, I'm suspicious you never saw the azola photos in Newgen's link above, so I'll link them in here:

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Oops. It's spelled "azolla".

And here's a the link to Newgen's azolla thread:

http://forums2.gardenweb.com/forums/load/ponds/msg0913300725060.html

Hi not sure if it is the Azolla like your photo but I am trying to get a photo if it, would not be possible to use a pump as a long long way from electricity supply the ponds in a field, I will catch some and then see if I can put a photo of it on here . . . Reb . . .

Try using a product called Sonar in order to get rid of it. It gets rid of a large spectrum of weeds throughout the whole pond.

http://www.lakelawnandpond.com/customerDefault.aspx

Shalom, not sure what the weed is - but you can get the best barley extract at Walmart, or any pharmacy you'll find it under the trade name of hydrogen peroxide. Same chemical