Toxic algae threatens Delta, Sacramento area waterways

The lake visitors call the “gem of Chico,” the local go-to location for a quiet and relaxing day trip on the waterfront, is infested with toxic algae, officials say.

The Butte County Public Health Department warned people on Monday to stay away from Horseshoe Lake after colonies of microscopic cyanobacteria grew out of control and ‘bloomed’ into toxic and potentially lethal algae, poisoning the waterway.

Harmful algae blooms, or HABs, are not new to the area — or to the Central Valley. This is the second alert of freshwater HABs recorded in the past 30 days in Butte County, and the 15th this year in the Valley.

While Sacramento County has less exposure to these toxic algae than other regions in California, local lakes are not safe from HAB exposure either, according to a report by the Sacramento Environmental Commission. “There is present a risk which may increase with higher temperatures, more frequent low flow conditions, and higher frequency of drought,” the commission warned in 2016.

In 2017, Laguna Joaquin in Rancho Murieta and the Stone Lakes national wildlife refuge in southern Sacramento County were affected by HABs. And just last summer, HABs were detected in Sacramento Lake near the Freeport Intake, in the Port of West Sacramento near the Washington Lake entrance, and in Arcade Lake.

The state’s Water Quality Monitoring Council collects and maps reports of HAB-related incidents, providing a better understanding of which areas are at greater risk of infestation. However, the council emphasizes that the “map only shows locations where harmful algal blooms (HABs) have been voluntarily reported... [and] a waterbody with no data is not an indication that a bloom is not present.”

The commission identified 10 waterways in the greater Sacramento area that pose a higher risk of HAB exposure:

• American River

• Sacramento River

• Cosumnes River

• Morrison Creek Group

• East Drainage Canal/Steelhead

• Creek/Dry Creek/Arcade Group • Deer Creek Group

• North Fork Badger/Laguna Creek/Deadman/Bear Slough Creek

• Delta waterways and sloughs • Folsom Lake

HABs have existed for millions of years and are essential to the freshwater ecosystem, according to a news release by the Butte County Public Health Department. However, since HABs thrive in “warm weather, stagnant water flows and excessive nutrient inputs,” more recent weather patterns caused by climate change and pollution are favoring their growth.