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. ie ammonia 0xygen ect.