Perplexing fish die-offs at three lakes along the Salt River during the past two months have scientists and others playing detective.
There was a fish die-off at Apache Lake during March, one at Canyon Lake around April 27 and the latest was in Saguaro Lake May 5. Another die off was reported at Apache Lake on May 18. Authorities are actively investigating the die-offs.
Larry Riley, the fisheries chief for the Arizona Game and Fish Department, says department biologists are working closely with scientists from other agencies, experts from Salt River Project, and university scientists to solve the mystery.
“Despite collecting lots of samples in the field and running a barrage of tests, we can’t point a finger and say, this is the definite culprit.‚ Just like in the detective stories, however, we do have a primary suspect we are continuing to investigate: a strain of toxic blue green algae called Cylindropsermopsis Raciborskii,”Riley says.
Cylindrospermopsis is an algae that produces two toxins called cylindrospermopsin and anatoxin-a. “Those toxins can, in the right concentrations, cause fish die-offs. This is emerging as the most likely causative factor for the fish kills. Note that I said most likely factor – I cannot provide a smoking gun, but all the pieces of this puzzle seem to be fitting together,” Riley says.
Game and Fish biologists have worked with experts at the Arizona Department of Environmental Quality at the three lakes to measure dissolved oxygen in the water, pH (acidity or alkalinity), and temperature, and have also tested for evidence of hydrogen sulfide. “We have taken field measurements from one end of these lakes to the other. We have also inspected recently dead or dying fish for evidence of disease: nothing,” Riley says.
Scientists also collected water quality samples and plankton for laboratory analysis. “The water samples are being analyzed for a broad range of contaminants, which is a very time intensive process. We’re looking for a needle in the haystack, and the needle may not exist,” Riley says.
The department has also worked closely with the U.S. Forest Service on the issue. Tonto National Forest Supervisor Karl Siderits says campgrounds are still open and there are still plenty of fish to be taken in the three lakes.
