Question
I have a pond that is bubbling around the falls.  The bubbles cover the top of the water and you can not see the fish.  They go away when I put food in the pond to feed the fish.  What can I do to stop stop the bubbles from forming?

Answer
The foaming is due to DOC, dissolved organic compounds.  The aeration of the waterfall makes them foam up.  Putting food in the pond shouldn't make the foam go away.  How big is your pond?  Do you do water changes?  Have you tested the water?  How big and how many fish are there?  If the pond is not overcrowded (the most common reason for foam), the foam may be due to the brand of fish food you're using.  This is what I wrote about DOC on my web site:

"Pond keepers often wonder about foam that can show up on the surface of ponds, often on hot days. This foam is the result of dissolved organic compounds (or DOC which stands for dissolved organic carbon) coming out of the water and creating foam. Moving water and aeration causes the DOC's to separate or fractionate from the water. There is a device called a foam fractionator that separates DOC's from water on purpose. Then, the foam is collected and discarded. Foam fractionators and protein skimmers, which are basically the same, are usually used in marine aquariums but can also be used in freshwater aquariums and ponds if desired.

On warm days, foam may froth at the base of waterfalls and fountains. This is especially common if the fish are ill or fish or amphibians have been spawning in the water. If there is a lot of foam, the foam should be removed if possible by dipping in a cloth or bucket to collect it. The DOC's come from multiple sources including, but not limited to, fish slime (which is produced in larger quantities if the fish have parasites, infections, viruses, injuries, etc.), sperm (and semen and eggs) [from spawning fish, toads (see here), frogs, etc.; very common], excess food (which is full of oily substances), rotting vegetation, and fish waste itself. My brother wants me to add humans (that would be me) in the pond (which are full of oily substances).

Doing water changes can reduce the DOC's concentration. Also, adding bags of fresh carbon will absorb some of the DOC's as well. In most cases, the concentrations of DOC's are low enough to not cause any threat to the animals in the pond. DOC's reduce the dissolved oxygen levels in water. In higher levels with lots of foam, the fish may have trouble breathing or otherwise show signs of stress. Foam can also occur in aquariums. It is usually a sign of stressed fish, spawning, or overfeeding, just as with ponds."

Good luck!