Redford,

I have heard of fiberglass water features doing that.

It might be a residue left from the manufacturing process. One suggestion is to scrub it with dish detergent and a brush, then rinse well and then see what happens.

Most commonly this is caused by dissolved organic matter (DOM). If the pond hasn't had a water change in 6 months or more, or there isn't a mechanical filter that gets cleaned often I would suspect DOM.

The foam can go away on its own as the dissolved matter decomposes into even smaller components. Or it can hang around. Scooping out the foam removes a lot of dissolved organic matter so speed up the process.

Most common fix is a water change. You can also build a "protein skimmer" or a "foam fractionator", same thing, different names.

I've had this problem many times but it always seems to go away after a couple of days. I think it actually helps get the bad gasses out of the water.

Also removes evil spirits.

Sorry Redford, I misunderstood your post. I thought this was a freestanding item, not part of the pond. Of course, dish detergent would not be a good idea in a pond. LOL

As it turned out. I had added a few limestone rocks to the pond to help the appearance of the not to realistic fibreglass. I think that the organic matter from the limestone breaking down was causing the problem, Once they were removed and the waterfall was given a good cleaning, the problem disappeared. Thanks to everyone for there great suggestions it really helped isolate the problem.

There's organic matter in limestone?