Castaic Lake, which was closed for 24 hours Thursday while helicopter crews treated the water with an algae-fighting chemical, is expected to reopen to the public early this morning, park officials said.
The annual application of copper sulfate, which diminishes the buildup of blue-green algae near the lake's surface, will benefit Southern California residents who drink the water, but it frustrated boaters, anglers and operators of personal watercraft who drove out to the reservoir Thursday only to discover the gates locked.
The airborne dispersal of the small blue copper sulfate pellets is a routine event and neither the chemical nor the algae itself presents a public health risk, officials of the state Department of Water Resources said. The agency manages the state aqueduct that feeds into the Castaic reservoir.
"Copper sulfate keeps the water cleaner and it makes it more drinkable," said Bruce Jackson, the operations superintendent at Castaic reservoir. "When you have an algae bloom that gets out of control, and that algae dies, it causes taste and odor problems with the water."
In high concentrations, copper sulfate can pose health risks to both humans and animals, but Larry Joyce, an environmental specialist with the Department of Water Resources, said that he knew of no instances in which the agency's use of the chemical to combat algae had led to problems.
"To be of significance to human health it would take concentration well in excess of what we use," Joyce said.
The agency will test water samples next week to determine whether the algae levels have dropped.
Scheduling of the chemical application is tied to water temperature. In normal years it is done in May before the busy recreation season begins, said Frank Gonzales, regional parks superintendent for Castaic Lake State Recreation Area. However, because of the high volume of water this year, the reservoir was slow to warm up, forcing officials to postpone the treatment until this week.
"We just found out they were going to do this on Tuesday," Gonzales said. "We put out signs to let people know the lake will be closed today."
Despite the signs and some news reports about the chemical treatment, hundreds of water-sports enthusiasts were caught off guard by the closure.
"We called yesterday and they didn't say anything about the lake being closed," said Dean Cassanelli, who drove to Castaic from North Hollywood.
"It's extremely disappointing," said Tamara Christian, also of North Hollywood. "I guess we're going to go over to [Lake] Piru, but it's probably going to be crowded because of all the overflow from Castaic."
Shelly Morgan, a cashier at the Lake Piru store, said the Ventura County lake was indeed much busier Thursday.
"We are getting some of their runoff," Morgan said. "We've had about double our normal number of boats."
Administrators at Lake Pyramid in northern Los Angeles County also reported a higher-than-average turnout Thursday.
Gonzales said park officials planned to reopen Castaic Lake today at dawn.