Question
Vt.pond  approx half acre was drained twice.    was ckear in the spring   until w eather warmed when it turned brown.  Lab tests indicated no abnormalities. no e-coli and pond is swimmable.Pond is mud bottom with aquatic life, crayfish, frogs.Water is now being aerated with a slight lightening in color.How can we get the pond back to its clear water color?

Answer
Thank you for your mail.
The answer is harder to tell from a distance, however I think there is no foil involved and a natural pond?
If so then you might think about the groundwater with some Iron in it.
Or do you fill the pond with groundwater, there can also be some iron in it.
Best way to tell is by placing the water in a very clear bottle.
Do not move it for approximate 1 night. If in the morning there is brown debris it is possible to be iron.
Also, trees can cause it.
I think however the first more common is iron in the ground and/or water.
Aeration can help, however will not clear the issue completely.
'that natures way...
If there is a foil / liner then it most common comes from the water.
Resolve this by letting the iron settle to to bottom if possible or by using tabwater.

Good luck!
regards,
Raf