Potentially harmful blue green algae found in Howarth Park’s Lake Ralphine

Santa Rosa Recreation and Parks officials are warning people to stay out of Lake Ralphine in Santa Rosa’s Howarth Park and to keep their pets away because of blue-green algae observed in the water there.

Though naturally occurring, blue-green algae — technically, cyanobacteria — can produce toxic substances that attack internal organs, resulting in severe illness or death if ingested.

Weekend boat rentals at the 25-acre lake in east Santa Rosa have been canceled since last weekend as a precaution and will remain canceled through at least Sunday, officials said.

Harmful blue-green algae blooms have been on the rise in California and around the West amid rising, sustained warm temperatures and high carbon dioxide levels in the atmosphere, scientists say. Increased nutrient loads, including nitrogen pollution, in waterways also fosters their growth, especially in calm, still waters.

Santa Rosa parks officials said park visitors should be aware that blue-green algae could be present in any local water body as seasonal temperatures warm.

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.