How someone’s pet goldfish destroyed an entire ecosystem at Maple Lake

Maple Lake has become infested with an invasive species: goldfish.

The Utah Division of Wildlife Resources says that the lake has become so overrun with goldfish that it’s become a crisis. The goldfish are polluting the water and using up so much of the food that the trout in the lake are dying off.

The only solution now, they say, is to wipe out every living animal in the lake and start over again.

Biologist Chris Crockett sat down with Dave Noriega and his special guest Amy Donaldson on KSL’s Dave & Dujanovic to talk about how a lake in Utah became overrun with fish we normally think of as pets — and just how hard it’s going to be to fix it.

A well-intentioned disaster

The infestation didn’t happen naturally. Goldfish don’t normally live in the lakes of the western United States, and it’s highly unlike that any pathways could have sent them into Maple Lake.

Instead, Chris Crockett says, the infestation most likely started with someone setting their pet goldfish free.

“I suspect that someone though they were doing their pet goldfish a favor,” Crockett says.

That act of mercy brought on an ecological disaster. Goldfish reproduce at extremely high rates; before long, they’d taken over the entire lake.

By 2015, anglers were reporting seeing goldfish in the water; and, not long after, they started seeing goldfish that had grown up to seven inches long. The fish just kept getting bigger and more plentiful after that, and now there are so many of them that anglers are having trouble keeping them off of their lines.

The goldfish now have such a huge presence in Maple Lake that the trout that normally fill its waters are starving to death. They’ve also muddied up the waters, making the lake completely inhospitable to other forms of animal life.

A drastic solution

At this point, Crockett says, there are no small steps that could clear the goldfish out.

In the past, conservation experts have been able to get goldfish out of other lakes by introducing a natural predator. In Maple Lake, however, the infestation is too wide-spread and the goldfish have grown too large for any controllable predator to take them out.

Instead, Crockett’s team is clearing the lake out altogether.

They have begun draining as much of the five-acre lake as they can. Now that the lake is significantly lower, they’re moving onto the next step: killing the fish inside with a chemicals called rotenone.

Next steps for Maple Lake

The chemical should wipe the goldfish of Maple Lake out completely, then break down within three days. After keeping the lake blocked off for 14 days, Crockett and his team will test the water to make sure it’s safe again. Once it is, they plan on refilling it with trout.

In the meantime, Crockett says that the rotenone water would be almost entirely harmless to humans, even if someone were to sneak into the blocked-off lake and drink the water.

“A person my size would have to drink about 100 gallons to have any sort of negative effect,” Crockett says.

Most other animals, likewise, should not be harmed. “A duck would have to drink about 7 or 8 gallons in one sitting to have an effect.”

After an expensive and drastic response, Maple Lake is expected to go back to normal. Crockett reminded our listeners, though, to keep their goldfish in their fish bowls.

More to the story

If you missed Dave & Dujanovic today on KSL Newsradio, you can still catch our interview with Chris Crockett on the Dave & Dujanovic podcast.

Dave & Dujanovic can be heard weekdays from 9 a.m. to noon on KSL Newsradio. Users can find the show on the KSL Newsradio website and app, as well as Apple Podcasts and Google Play.