Golden alga is believed to be the culprit behind thousands of fish dying on a 20-mile stretch of the Salt River, where it flows into the east side of Roosevelt Lake.
Lab tests of the water and collected dead fish revealed high concentrations of Golden alga, according to a news release from Arizona Game and Fish. Golden alga produces a toxin that impacts the gills of fish and causes them to suffocate.
The die-off has included species such as catfish, carp, bluegill, red shiner, largemouth bass, buffalo fish and crayfish.
Game and Fish began receiving reports from the public about dead fish on Wednesday, and dispatched a team of biologists to investigate.
Golden alga was first reported to cause extensive fish-kills in the 1930’s and has been found in California, Nevada, New Mexico, Texas, and at least a dozen other states. Biologists have not yet determined if Golden alga occurs naturally in Arizona, but it has been identified in more than 20 lakes statewide since 2003, the release said.
Biologists do not yet know what causes Golden alga to produce the toxin that is fatal to fish, crayfish, mussels, and all gill-breathing creatures. But, experts have found a connection between extended drought, elevated salinity in waterways, and fish-kills caused by the toxins in Golden alga.
“We believe that drought conditions and increased salinity may create an environment where Golden alga can thrive,” Kirk Young, a fisheries biologist with Game and Fish, said in the release. “Golden alga is found most often in waters with especially high salinity.”
He pointed out that the Salt River was named for the salt springs that are found upstream and responsible for the water’s high salinity in periods of low flows. The salinity in the Salt River is more than three times the concentration currently found in Roosevelt Lake.
According to the release, biologists do not think that the Golden alga problem will extend into Roosevelt Lake any time soon, because the high salinity and algae concentrations found in the inflow water from the Salt River are diluted when mixed with water already in the lake, making it less than toxic to fish.
Game and Fish plans to continue investigating and will monitor waterways along the Salt River, including Apache, Canyon and Saguaro lakes where Golden alga is believed to still exist, but is currently in low concentrations.
If drought conditions persist, downstream reservoirs could be at risk in the future, the release said.
So far, no adverse health effects have been noted for humans or non-gill-breathing wildlife that come in contact with waters experiencing a Golden alga toxin bloom. But Game and Fish says the public should not eat any dead or dying fish found anywhere regardless of the cause. However, it’s OK to continuing eating you catch, as long as the fish are properly cleaned and thoroughly cooked.