Winter Season is also Golden Alga Season
You’ve probably heard about Golden Alga (GA) by now… and if not, you probably will. For close to a month we’ve experienced a slow but steady fish kill at Veteran’s Oasis in Chandler. What made it particularly frustrating is that ongoing sampling by the lake consultant found no evidence of Golden Alga (GA), and our on-site sampling prior to stocking fish revealed good water quality parameters. Last week we were able to detect GA in samples we collected at the lake, which now explains the catfish and trout that had been dying.
We figured the time was right to share some additional information about this pesky form of algae. Golden alga (Prymnesium parvum) is a single-celled species of algae that is found in waters all around the world. In Arizona, it was first discovered in 2005 at Water Ranch Lake in Gilbert. How it got here is still unknown, but like all aquatic invasive species, this organism can easily spread and affect the fisheries. As chlorophyll-containing organism it can produce its own food like any other plant by using sunlight and nutrients, but GA can also release chemical compounds that combine with minerals in the water to produce toxins that cause fish kills in order to release nutrients and feed. The good news is that GA is harmless to air-breathing organisms.
When GA “blooms” (enters a phase of rapid growth & reproduction) it can produce toxins that harm or kill gill breathing organisms like fish, freshwater mussels & clams, and the gill-breathing juvenile stage of frogs and other amphibians. A GA fish kill may last for days, weeks, or months, and sometimes only a portion of a lake is affected, but the location can change from one day to the next. This is exactly what makes detection and confirmation a challenge – like we had at Veteran’s Oasis. Furthermore, even if you confirm the presence of GA within a water, it doesn’t mean that it is producing the toxins. Scientists are still working to develop an accurate method of detecting GA toxins. Thus, the presence of GA does not guarantee that it will kill fish. Many waters in the southeast USA as well as here in Arizona have never experienced a fish kill despite having GA.
GA has been confirmed in many of the Community Fishing Program waters as well as Roosevelt Lake, Apache Lake, Canyon Lake, Saguaro Lake, lower Salt River, Kearney Lake and Topock Marsh along the Colorado River. Community Fishing Program waters that are known to have (or had) GA include Tempe Town Lake, Riverview Lake, Water Ranch Lake, Freestone Ponds, McQueen Pond, Veteran’s Oasis, Cortez Lake, Papago Ponds, Encanto Lake, Desert West Lake, and Alvord Lake. Symptoms of GA include dead or dying fish, usually multiple species and sizes; Water that has a golden, copper, yellowish, or tea-colored hue; Bubbles that stick on the water surface like a soap or foam, usually near aeration devices, fountains, or waterfalls; and Lethargic fish that don’t spook or flee when you approach.
GA blooms are more likely to occur in cold weather, and sometimes taper off as the water warms and other species of algae (green or blue-green) become more active. Treatment usually involves application of an algaecide such as copper sulfate. Unfortunately at this point there is no magic cure to remove GA from the waters it occupies. All we can do is prevent the spread to the best of our abilities. Anglers can help by making sure equipment such as boats, livewells, boots, and waders have been thoroughly dried between use in different waters. Golden Alga is a tiny organism that has the potential to pack a deadly punch. Unfortunately it is spreading, but rest assured it doesn’t automatically mean doom and gloom for the infected water. And don’t worry, the GA is not harmful to pets or other terrestrial wildlife if they contact or drink the lake water.