A 70 year old, 8 acre strip mine lake's water has turned a very peculiar orange rust color, even pretty visible through the ice.
Any thoughts as to what this is? or what is causing this to happen? The water is typically pretty fertile and green, and there are a lot of trees around.

try this thread
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Bill Cody looked at the water and found that "The problem in your sample is a filamentous planktonic bluegreen (Cyanobacteria) algae called Planktothrix rubescens. Previously it was called Oscillatoria rubescens."

If anyone has suggestions on what can be done this time of year to combat Planktothrix rubescens, please send them this way!

Did Bill say if it is a cold water species that will dye back when the water warms and the green plankton takes over ?

n8ly,
I hate to throw in my two cents, since I am an ignoramus for the most part and so new to all of this. But did you say that this was lake formed from an old strip mine? THe reason I ask is that when I was around a lot of old strip mines and pits in East TN we had a significant problem with acid seepage from the underground mine. It always was obvious because it painted an orange strip down the mountain side wherever the water flowed. It would also turn all the rocks rust colored in the bottom of any creek that it found its way into.

It is an old strip mine, but I dont think acid seepage is the problem. The bottom is very dark rich sediment and the water doesnt get much wind action from being tucked back into the trees.

The algae is a cold water algae that is blooming up on the surface now, but will retreat to or below the thermocline for the summer. I have spent a few hours today researching what can be done.

Basically the algae could release its toxins at anytime, but especially when it dies. (shouldnt treat it with algaecide) BUT It is so thick at the surface that it is blocking the sunlight from the rest of the water. So there is a good chance the fish are going to die soon no matter what I do? Installing an aeration system this time of year could create open water and allow sunlight to penetrate better, but that comes with another set of risks for the fish.

Did Bill say it was toxic ? If so I am surprised it has not killed the fish in prior years.

A lot of things depend on how toxic the bloom becomes. The algae is known as a toxin producing species.

n8ly, As far as aerating this 8 acre pond consider just opening 2 areas at opposite ends this may provide the needed haven and not super cool the entire bottom.

Bill Cody said it right, that species is know to have the capabilities to produce the toxin and this strain may not have enough toxins associated with it. They also carry different strains of toxins from simple skin irritating toxins to the most dangerous of toxins being neuro. Those are typically seen in the Outback.

Ted nailed it that if you were to simply install two diffusers not at maximum depth at both ends, that will be more than enough to open some holes and not compleletly kill the algae or super cool the pond. Ted is the cold water aeration expert with his experiences in his own ponds.