San Diego cautioned visitors about an algae bloom at Lower Otay Reservoir after monitoring identified conditions that could pose a health risk.
Harmful blooms can produce toxins and may affect people, pets and wildlife. Public guidance typically focuses on avoiding contact with discolored water and keeping animals away until testing shows conditions have improved.
The warning demonstrated the public-health role of routine reservoir monitoring. Visibility can change quickly, so laboratory results and updated advisories remained more reliable than appearance alone.