A California colleague of ours tells a very fun story about this issue. He’s a much better story teller, and it’s a bit longer story, but here’s a consolidated version of a conversation he had with an elderly lady that had a fairly new ecosystem pond replacing an old concrete pond.
Client (calling contractor in a bit of a panic): Today, I woke up and there’s a bunch of foam in my pond! What’s going on?
Contractor: Does it smell a bit fishy, like the ocean?
Client: Why, yes, it does.
Contractor: Well, ma’am, that means your fish are happy with their new home.
Contractor: (after a couple of more attempts to be “delicate”) It’s sperm.
[Silence for a few seconds]
Client: What kind of sick son of a b*&ch would do that in my pond?!??
Contractor: (stifling hysterical laughter) No, ma’am, it’s your fish spawning.
Cue light bulb over client’s head
So, the moral of the story is that it’s just your fish “getting’ busy.”
What should I do about it?
Absolutely nothing. It should dissipate in a few days, depending on your filtration system. If you don’t have Gambusia in your pond for vector control, you may have baby fish swimming around in the not too distant future. If you have Gambusia, they will eat the fish eggs before they have a chance to hatch. Caviar is their second favorite food, after mosquito larvae.
If your fish are happy and feel safe in their home, this will happen. Spring is typically the season, when every creature seems to be twitterpated, but it may happen again in the Fall, too.
You may also notice that one or two of your fish appear to be “picked on” just before this happens. Those are the females. Unfortunately, they don’t lay eggs easily, and the males kind of beat up on them to help them release the eggs for fertilization. As a friend of ours once said: “Life around a pond is both beautiful and brutal.” It’s all just nature taking its course.