Friday, August 6, 2021

City of Austin investigates potential harmful algae in Bull Creek

On Thursday, August 5, the City of Austin was informed that a person developed symptoms that could be associated with exposure to harmful algae after playing in Bull Creek over the weekend. The City is actively investigating the situation.  

At this time, we cannot confirm the presence of harmful algae at Bull Creek or whether the illness was caused by exposure to algae. The creek does not have any obvious signs of harmful algae. The City of Austin took algae and water samples this morning, and we expect to have preliminary lab results next week.  

There can be various risks associated with swimming or wading in creeks and lakes. Natural water bodies contain microscopic organisms such as bacteria and parasites. There can also be physical dangers with uneven depths, debris, slippery surfaces, and strong currents. We advise people and pets to avoid warm, stagnant water. Steer clear of any discolored or foul-smelling water. It is always a good idea to rinse off after being  in a natural water body. Avoid swimming for a few days after heavy rainfall when bacteria levels tend to be higher. 

Cyanobacteria, or blue green algae, occurs naturally in Central Texas waterways. Some species can produce toxins under certain conditions. It is impossible to tell if toxins are present by looking at algae, so assume that all algae may have toxins and avoid direct contact. 

Toxins were first detected in algae in Lady Bird Lake in 2019. The City of Austin ordered specialized lab tests after being told that a dog died after swimming in Lady Bird Lake. We are currently monitoring Lady Bird Lake and Lake Austin for harmful algae every other week. This summer we have detected low levels of dihydroanatoxin in algae at Red Bud Isle since June. We have had isolated positive tests for dihydroanatoxin at Walsh Boat Landing in June and Jessica Hollis Park in March.   

To date, the City of Austin has only detected toxins in mats of algae that can be found growing on the bottom of the lake or floating on the surface. This means exposure would come through touching or swallowing visible algae. The City is aware of five dogs who died after swimming in Lady Bird Lake in 2019, and warning signs have been posted there for this reason.  

In people, symptoms of exposure to harmful algae may include: 

  • Dermatologic signs or symptoms such as rash, irritation, swelling, or sores 
  • Gastrointestinal signs or symptoms 
  • Respiratory signs or symptoms 
  • Fever 
  • Headache 
  • Neurologic signs or symptoms 
  • Ear symptoms 
  • Eye irritation 

In dogs, symptoms may include:   

  • Excessive drooling, vomiting and diarrhea 
  • Foaming at the mouth 
  • Jaundice and hepatomegaly 
  • Blood in urine or dark urine 
  • Stumbling 
  • Loss of appetite 
  • Photosensitization in recovering animals 
  • Abdominal tenderness 
  • Progression of muscle twitches 
  • Respiratory paralysis 

We encourage the public to call 3-1-1 or 512-974-2000 to report any illnesses in either people or pets from exposure to harmful algae. More information about harmful algae is at

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