**Austin Heat: Is City Sunscreen Hiding Toxic Algae?**

By Franklin Everett Shaw

January 22, 2026

That greenish scum clinging to the rocks at Barton Springs? It might look natural, but it could be a silent threat lurking beneath the surface.

Austin’s beloved swimming holes and even backyard pools are increasingly vulnerable to toxic blue-green algae, scientifically known as cyanobacteria. The perfect storm of sunscreen runoff, rising temperatures, and stagnant water creates a breeding ground for these potentially harmful organisms. Let’s dive into how to protect yourself, your family, and your pets from this growing environmental concern.

Cyanobacteria aren’t actually algae; they’re bacteria that photosynthesize, like plants. They thrive in warm, nutrient-rich water, and Austin’s climate and popular swimming spots provide just that. Sunscreen, while essential for protecting our skin, washes off in the water, releasing chemicals like oxybenzone and octinoxate. These chemicals, along with other pollutants, act as fertilizers, fueling algae blooms.

Barton Springs Pool and Zilker Park’s Lady Bird Lake are prime examples. The constant influx of swimmers slathered in sunscreen, combined with the natural runoff from the surrounding urban environment, creates a nutrient-rich soup that cyanobacteria love. The Lower Colorado River Authority (LCRA) regularly monitors these areas, but blooms can appear and disappear quickly, making constant vigilance crucial.

So, how do you identify these potentially dangerous blooms? Look for these telltale signs:

• Appearance: The water may appear pea-green, blue-green, or even reddish-brown. It can look like spilled paint or thick scum floating on the surface.
• Smell: Some blooms have a musty or earthy odor.
• Location: Blooms often accumulate in stagnant areas or along shorelines.

If you spot something suspicious, do not swim or allow your pets to enter the water. Report the bloom to the City of Austin or the LCRA immediately. It’s always better to err on the side of caution.

The dangers of cyanobacteria are real. Exposure can cause skin irritation, nausea, vomiting, diarrhea, and even liver damage in humans. Pets are particularly vulnerable because they often drink the contaminated water while swimming or playing. In severe cases, cyanobacteria toxins can be fatal to animals.

Beyond public waterways, your own backyard pool or water feature can also become a breeding ground for toxic algae. Here’s a DIY guide to keeping your personal water features clean and safe:

1. Regular Testing: Invest in a pool testing kit and check the water chemistry regularly. Maintain proper chlorine or bromine levels to kill algae.
2. Phosphate Removal: Phosphates are a key nutrient for algae growth. Use a phosphate remover to starve the algae. You can find these at most pool supply stores.
3. Circulation and Filtration: Ensure your pool’s circulation system is working properly and that the filter is clean. Good circulation prevents stagnant water, and a clean filter removes debris that algae can feed on.
4. Algaecides: Use algaecides as a preventative measure, but be sure to follow the manufacturer’s instructions carefully. Overuse can lead to chemical imbalances in the water.
5. Regular Cleaning: Brush the walls and floor of your pool regularly to remove algae buildup. Vacuum the pool to remove any debris.
6. Consider a Saltwater System: Saltwater pools use a salt chlorine generator to produce chlorine, which can be gentler on the skin and less likely to cause algae blooms than traditional chlorine systems.

A common mistake is neglecting to clean the pool filter regularly. A dirty filter is less effective at removing debris and can actually contribute to algae growth. Another pitfall is relying solely on chlorine without addressing other factors like phosphate levels and circulation. A balanced approach is key.

For smaller water features like fountains or ponds, consider using barley straw. Barley straw naturally decomposes and releases compounds that inhibit algae growth. Simply place a mesh bag filled with barley straw in the water feature.

One specific challenge in Austin is the hard water. Hard water contains high levels of minerals like calcium and magnesium, which can interfere with the effectiveness of chlorine and make it more difficult to control algae growth. Consider using a water softener or a calcium hardness reducer to improve water quality.

Let’s talk about sunscreen. While we can’t avoid using it altogether, we can make more responsible choices. Opt for mineral-based sunscreens containing zinc oxide or titanium dioxide. These are less harmful to aquatic ecosystems than chemical sunscreens. Apply sunscreen at least 15 minutes before entering the water to allow it to absorb into your skin. Reapply frequently, especially after swimming or sweating.

Consider using rash guards or other protective clothing to reduce the amount of sunscreen you need. These provide excellent sun protection without releasing chemicals into the water.

Beyond individual actions, community involvement is crucial. Support local initiatives aimed at reducing pollution in Austin’s waterways. Advocate for stricter regulations on sunscreen ingredients and better stormwater management practices.

The fight against toxic blue-green algae is an ongoing battle. By understanding the risks, taking preventative measures, and making informed choices, we can protect ourselves, our community, and the natural beauty of Austin for generations to come. Let’s keep our swimming holes safe and enjoyable for everyone.