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Algal Toxin Kills Thousands Of Fish In Apache Lake

Threadfin shad
(Photo by René Reyes - U.S. Department of Interior)
Threadfin shad.

In the spring, a young man's fancy lightly turns to thoughts of shad. But not at Apache Lake — at least for now, says the Arizona Game and Fish Department.

A population explosion of golden algae, a fast-growing invasive plant, has killed thousands of threadfin shad and some gizzard shad at the lake.

The same problem afflicted fish in Saguaro, Canyon and Apache lakes 10 to 15 years ago.

The single-celled plants exude toxins harmful to gill-breathers like fish and clams, but pose no risk to humans or pets.

Golden algae seem to thrive in warmer, saltier waters, so officials hope that recent heavy rains might help stem their rapid expansion. In the meantime, the area remains open, and officials say that healthy fish caught in the lake are safe to eat.

News Science
Nicholas Gerbis was a senior field correspondent for KJZZ’s Arizona Science Desk from 2016 to 2024.