Thursday, June 9, 2022

Harmful algae present at Red Bud; Austin expands Phoslock treatment of Lady Bird Lake

With the coming of hot temperatures and drought conditions, the risk for harmful algae in our natural waterways increases, and today, Watershed Protection received lab results indicating the presence of Dihydroanatoxin A in its first algae sample. The sample was taken from Red Bud Isle on May 30, 2022. This toxin has been detected in previous years in algae samples from Lady Bird Lake and is a potent neurotoxin.

Some species of Cyanobacteria, also called blue-green algae, can produce various toxins under the right conditions. When this occurs, it is called a harmful algae bloom or proliferation. The toxins can make people and pets sick. In 2019, several dogs died after swimming in Lady Bird Lake during a harmful algae bloom.

Treating Lady Bird Lake with Phoslock may help prevent or slow down the growth of harmful algae in some areas of the lake. Phoslock is a clay material that binds to phosphorus, a key source of nutrients for algae. Once bound into a mineral form, the phosphorus becomes unavailable to the algae. Phoslock lowers nutrient levels in the lake and essentially robs the algae of one of its primary food sources, slowing down its spread.

Last year, Watershed Protection applied Phoslock to over 22 acres of Lady Bird Lake near Red Bud Isle. The results were encouraging with a 40% reduction in the amount of phosphorus available to algae. Sediment testing in May of 2022 showed that the reduction in available phosphorus had persisted over nine months.

This year, Watershed Protection will expand the Phoslock treatment to include the north shore of Lady Bird Lake from I-35 to the lagoon by the Festival Beach boat ramp. This area was chosen due to the results of algae samples collected from the area last year. Multiple toxins were present in some samples. Treatment will occur on Monday and Tuesday of next week. The department will also reapply Phoslock at Red Bud Isle on Wednesday.

The department will apply 30,000 pounds of Phoslock at each location next week. There will be a second treatment later in the summer at both locations. The cost for all the treatments, testing and lab work is $300,000.

During treatments, boaters should avoid the treatment area and keep plenty of distance from the barge applying the Phoslock. The barge will be spraying a gray slurry into the lake that will temporarily cloud the water. The substance is safe for humans, the environment and wildlife, and will settle to the bottom in a few hours.

Although this treatment should help reduce the amount of harmful algae this summer, it may still be present. Other dangers, such as bacteria and parasites, may also be present. When enjoying the outdoors, look for water that is cool and flowing. Avoid contact with algae, rinse after swimming in natural water bodies and do not allow dogs to lick their fur prior to rinsing. Do not enter water that is warm, stagnant, or contains scum, film or algae. Also stay out of water if it has rained in the past three days or if there are many dogs present.

Watershed Protection has resumed biweekly monitoring of Lady Bird Lake and Lake Austin for harmful algae for the summer. Results of sampling are posted at Please be aware that there is a one-to-two week turn-around time for results. Environmental conditions may change rapidly, and conditions may vary throughout the lake. Visitors to the lake should assess the conditions at the time of their visit, avoid shorelines and backwater areas and treat all algae like it may be toxic.

July 4th, 2022: Independence Day Holiday Closures

  Several City of Austin offices and facilities will be closed today, Monday, July 4 in observance of Independence Day Parks and Recreation ...