Warm weather earlier this fall and drought conditions have made toxic blooms of blue-green algae more frequent in the East Bay Regional Park District recently, including several sites in the Tri-Valley.
Cyanobacteria -- otherwise known as blue-green algae -- is present in the Del Valle Reservoir at Lake Del Valle and the back lakes area and arroyo at Shadow Cliffs Arroyo, along with a number of other East Bay parks, according to officials, who blamed the increased blooms on "the drought and unusually warm weather conditions."
Toxins have also been detected at Lake Del Valle but not at Shadow Cliffs; officials said. Visitors are advised to "avoid any contact with cyanobacteria or scums, and keep dogs away" from Lake Del Valle, as well as from the water in the arroyo. Swimming is not currently permitted in Lake Del Valle due to COVID-19 restrictions.
The lake trail at Shadow Cliffs, and the Visitor Center and Ohlone Wilderness Trail at Lake Del Valle remain closed, though the Dog Trail at Del Valle Regional Park is scheduled to reopen Nov. 13. The Del Valle campgrounds and day use (east side only) remain at a 50% capacity limit.
EBRPD regularly monitors its lakes and shorelines and posts warnings and closures when needed. For more information, visit ebparks.org.