Authorities have not yet determined the source of contamination of an E. coli outbreak detected on a stretch of the South Yuba River in Nevada County, but the water has now returned to a safe condition, environmental health officials said Tuesday afternoon.
“Most recent water samples came back as safe for recreational use,” Nevada County said in an update just before 1:14 p.m., announcing a no-swim advisory had been lifted. “Cause of the plume is still under environmental review.”
The plume of discolored water was detected Friday evening near the Highway 49 bridge.
The first round of water samples taken near that area tested positive for double the level of E. coli considered acceptable by the Environmental Protection Agency on recreational waterways, prompting the Nevada County Office of Emergency Services to issue a no-swim advisory from the town of Washington up to and including Englebright Lake.
The county said in a news release Monday evening that the discoloration observed at the river was “not due to the E. coli originally found, and it is unknown if the E. coli is correlated with the plume.” E. coli levels decreased between Saturday and Monday’s tests at the river and Englebright Lake, but the no-swim warning stayed in place until Tuesday afternoon.
Water samples were taken from both the river and the lake, and both were deemed safe for recreational use.
Nevada County is working with numerous local, state and federal agencies to discover the source of the E. coli contamination. Environmental health officials are also awaiting results from additional toxic metals test conducted over the weekend. Those tests generally take three or four days to complete.
Arsenic, lead and mercury sometimes flow into the river due to the area’s extensive history of mining operations. Mining sediment could account for discolored or murky waters, but not for E. coli bacteria, which is an indication of fecal contamination often caused by either fresh sewage or high concentrations of animal waste.
The Yuba County Office of Emergency Services had issued its own no-swim advisory for the Middle Fork of the Yuba River starting Sunday morning, but the advisory was lifted that afternoon as the water cleared up.