Published June 9, 2026 at 11:06 AM CDT
Call it Austin’s grossest rite of spring: Toxic cyanobacteria, also known as blue-green algae, has awoken from its cold-weather slumber to spread in local lakes and waterways for another year.
Austin’s Watershed Protection Department says its staff has observed thick “mats” of the bacteria floating near Red Bud Isle on Lady Bird Lake and near Walsh Boat Landing on Lake Austin.
Those mats emerge from below to float on the water’s surface. They often have a dark greenish hue and a slimy puke-like consistency. They can be toxic to animals and humans and become entangled in other water vegetation.
In a press release Tuesday, Watershed Protection urged people to avoid all contact with the algae and to avoid “stagnant, warm or murky water” and water with “scum or surface film.”
City of Austin
In past years, blue-green algae killed several pet dogs and caused the closure of popular swimming spots in Austin.
It first appeared in local waterways in 2019 after destructive floods upstream injected massive amounts of storm runoff containing fertilizers and septic waste into local lakes.
“If you or your pet experiences sudden, unexplained illness after swimming, contact your medical provider or veterinarian immediately,” the city advised.
The algae loves warm water and typically spreads as the weather heats up.
If you know of a person or pet that may have become sick from algae exposure, Austin Public Health asks that you report the case through its online form.
Austin Watershed Protection said it has submitted six samples taken from local lakes to laboratories for further testing.
You can find more tips for protecting yourself and your pets from the algae here.