A plant that lives year-round in the Salt River caused the death of thousands of fish last week, officials believe.
Severe drought and high salinity levels apparently caused the Golden alga to bloom, clogging fish gills and causing the fish to hemorrhage and die, said Jim Paxon, chief of information with the Arizona Game and Fish Department.
“The thing that will cure that is about two inches of rain,” he said.
Anglers found thousands of fish dead in various pools along a 20-mile stretch of the Salt River beginning July 4.
Water and fish samples confirmed high concentrations of Golden alga is likely the cause of the die-off.
Golden alga produces a toxin that clogs fish gills, suffocating the fish.
Starting in the 1930s, biologists connected Golden alga to extensive fish-kills in California, Nevada, New Mexico, Texas and a dozen other states.
It is unclear if the plant occurs naturally in Arizona, but biologists have found it in more than 20 lakes statewide since 2003.
Despite extensive research, biologists do not yet know what causes Golden alga to produce the toxin fatal to all gill-breathing creatures, according to a press release. However, experts have noted a connection between extended drought and elevated salinity, or salt levels.
“We believe that drought conditions and increased salinity may create an environment where Golden alga can thrive,” said Kirk Young, a fisheries biologist with Game and Fish.
“Golden alga is found most often in waters with especially high salinity.”
The salt level in the Salt River is more than three times that found in Roosevelt Lake. The river gets its name from numerous upstream salt springs.
Although the Salt River flows into the east end of Roosevelt Lake, biologists do not believe the alga will extend into the lake. The lake water reduces the high salt and algae concentrations in the river water.
The die-off included species of catfish, carp, bluegill, red shiner, largemouth bass, buffalo fish and crayfish.
To date, no humans or non-gill-breathing wildlife exposed to Golden alga have had side effects. However, Game and Fish advises the public not to eat any dead or dying fish found anywhere regardless of the cause.
People can continue to eat the fish they catch, as long as the fish are properly cleaned and thoroughly cooked, officials said.
Game and Fish continues to monitor the waterways along the Salt River, including Apache, Canyon and Saguaro lakes, where Golden alga is also found, but has not yet bloomed. If the drought persists, these waterways could be at risk.
No one knows how to eliminate the alga from reservoirs and rivers.