A rapacious, fish-killing algae linked to the recent loss of more than 1,000 fish in a Gilbert lake also has been found in Saguaro Lake. The fast-spreading species of golden algae could do extensive ecological damage, officials said.
Arizona Game and Fish Department officers found 2,000 dead fish in Saguaro Lake earlier this week, said biologist Eric Swanson, the agency’s urban fishing manager.
The fish were threadfin shad, the type of fish typically the first to be affected by the toxic algae, he said.
Gilbert is draining more than half of the 5-acre lake in its Riparian Preserve at Water Ranch to try to kill golden algae that was found there in January and has already killed two-thirds of the lake’s fish.
The two occurrences are the first known infestations in Arizona of prymnesium parvum, which has killed tens of millions of fish in other states in the past two decades, Swanson said.
More testing for the algae will soon be done in Roosevelt, Apache and Canyon lakes, officials said. The lakes, along with Saguaro, are part of the Salt River watershed in the Tonto National Forest that runs into the East Valley.
The state now faces a difficult battle against the resilient species, said David Walker, an aquatic ecologist in the University of Arizona’s Department of Soil, Water and Environmental Sciences.
"It won’t be easy to contain," said Walker, an algae specialist who conducted tests confirming the algae has arrived in Arizona. "The odds are it will spread."
Texas is the hardest hit of at least nine states where it has been found. Since the mid-1980s, the algae has spread in Texas to five major river systems, more than 20 reservoirs and many lakes, killing almost 18 million fish, according to the Texas Parks and Wildlife Department.
Its appearance in Saguaro Lake heightens the ecological threat significantly.
"It’s easier to control in an urban lake, where you can drain water and put new water in. You can’t do that in a large reservoir like Saguaro," Walker said. "The treatment is not easy and not (financially) feasible."
A number of university and private research programs are seeking methods to stop the spread of golden algae, "but so far there’s no silver bullet," said Tom Harvey, spokesman for the Texas agency.
The single-cell, microscopic algae releases toxins that can prevent gillbreathing organisms such as fish and clams from drawing oxygen from water, suffocating them. Golden algae has no apparent ill effects on humans or other animals.
Water Ranch Lake in Gilbert will be drained to as much as 40 percent of its capacity, said Kenny Martin, Gilbert parks superintendent. Sunlight should dry up much of the golden algae in the exposed part of the lake. In addition, a chemical algaecide will be applied and the lake will be refilled with fresh groundwater, Martin said.
The process is expected to take three to four weeks, he said.
Game and Fish has canceled a routine fish stocking of Water Ranch Lake this month and next.
Officials said they’re confident the treatment will remove the golden algae from the lake, but there’s no assurance the problem won’t reoccur, or that it isn’t already spreading.
A single drop of water can hold more than 500 algae cells, Swanson said. That means it can be carried easily by birds moving from one lake, river or canal to another. Experts suspect it can also be spread by latching onto watercraft or fishing equipment that’s taken from one waterway to another, he said.
Golden algae is known to spread particularly fast among threadfin shad, a small fish eaten by many larger fish.
"We have shad by the millions in Saguaro," Swanson said.
While the algae does not present a health hazard to humans, "common sense says to be wary," he said.
Golden algae’s toxins do not get into the flesh of fish and cannot be transferred by consuming the fish. But Game and Fish still recommends not picking up, taking or consuming dead fish or those appearing ill.
"The sky is not falling. But there’s a new environmental issue that we have to deal with," Swanson said.
State health and environmental officials are alerting parks and lakes managers throughout the Valley to look for signs of golden algae, he said.
Indications typically include water turning either yellowish or reddish-brown. When the algae is heavily concentrated, it can create a soapy-looking foam on water surfaces, experts said.