UC Davis issued a caution today (Sept. 8) to people visiting the Arboretum Waterway with their dogs: Keep your animals away from the water — do not let them go in it, do not let them drink it — due to the presence of cyanotoxins.

These toxins from microscopic cyanobacteria can be rapidly lethal to dogs that ingest the contaminated water. The concentration at this time is low, said Nina Suzuki, waterway steward for the Arboretum and Public Garden. Still, dog owners should be cautious.

Blooms of algae and cyanobacteria are common in creeks, rivers, ponds and lakes, especially in nutrient-rich waters in summer. (The Arboretum Waterway, despite its name, is a pond — it has no natural flow.)

Cyanobacteria live throughout the water column, not just as “scum” on the surface. So it is difficult to tell if water is contaminated just by looking at it. The solution? Just don’t go in the water.

“This timing is typical for the cyanotoxins in the Arboretum Waterway,” Suzuki said. “The pattern in the last three years has been that the toxins aren’t present in detectable amounts until August.”

And, so, upon observing an algal bloom last month, she collected a water sample and sent it in for analysis. The results came back Sept. 5.

“For context, the state water board has three tiers, or trigger levels (caution, warning and danger), for advisories based on the concentration of toxins found in the water,” Suzuki said. “The lab results from our sample are at the low end of the caution level.”