If your pond has not been the target of a practical joke chances are the foam you’re experiencing is not a health hazard to the fish. It is a sign of other things that may be happening in your pond.
If it’s spring and the water has just warmed up the first thing that comes to my mind is that your fish have been doing the “wild thing” in your pond. They’ve been spawning. Fish usually prefer to rendezvous at daybreak or at dusk so if the foam sighting is just after these hours that’s a good sign that all is well. Another indicator is if the fish have been wallowing in the plants or if several fish seem to be chasing one. If this is the case the foam you see is actually fish sperm. Lovely mental picture — isn’t it?
Another possibility is that your pond is doing it’s protein skimming “thing”. The pond naturally traps proteins and other organics that would end up as ammonia and nitrites in bubbles that form wherever air and water “collide”. This would be most noticeable at the base of the waterfall. It’s easier for soft water to form bubbles than it is for hard water so the hardness of your water contributes to the foam that you see. Metro Atlanta’s water tends to be very soft. If the foam is just located at the base of the waterfall chances are that the pond is skimming proteins from the water. The best thing for you to do is skim off the foam with a net and dispose of it or let your skimmer take it into the filter to be flushed out of the system.
When fish are stressed they emit slime. This can contribute to higher amounts of foam in the water because slime is organic. If you suspect this to be a contributing factor to your foam it is best to check for stress factors. Test the water for ammonia, nitrites and pH. If possible perform a fish mucus scraping to either give conclusive evidence or rule out the possibility of parasites.
If all you’re wanting to do is get rid of that ugly foam we have the product that works instantly to remove it. It’s called Doc’s DeFoamer.
If your pond is a victim of a practical joke and someone has emptied a bottle of suds into the water — treat it as a fish emergency. Make a 90% water change immediately.