According to the City of San Marcos Parks and Recreation Department has taken a lot of questions about the presence of Blue Green Algae in the San Marcos waterways following the news in Austin about health and safety concerns for dogs in Lady Bird Lake.
Clearing up the concerns…
The San Marcos River is home to many different kinds of algae, and this includes Blue Green Algae. However, the algae’s toxicity comes into play only when the algae blooms.
Historically, indicators of algae blooms have typically been below limits of quantitation in the San Marcos River, because its physical and chemical characteristics do not create a good environment to produce Blue Green Algae blooms.
Our river is mostly fed by the Edwards Aquifer, whose constant 72 degree temperature is significantly lower than other lake, streams, and ponds, making blooms much less likely.
The currents are also swift, giving algae and other microorganisms less stability to grow.
Lastly, the San Marcos River typically has much lower levels of Nitrogen and Phosphorus than other bodies of water, which Blue Green Algae needs to survive and bloom.
Although the city says they can never really rule anything out, the source of the San Marcos River is substantially different from the lakes and rivers in Austin, and much less conducive to algae blooms.