A California reservoir is full and spilling for the first time in nearly 2 decades

The series of atmospheric river storms that have hit the Central Coast have pushed another San Luis Obispo County reservoir to full capacity — and it’s spilling for the first time in about 18 years.

Whale Rock Reservoir near Cayucos along San Luis Obispo County’s northern coast has gained about 3.5 billion gallons since Jan. 1, according to data from the city of San Luis Obispo. It now holds 38,967 acre-feet of water, according to the city.

It went from 72.1% capacity to 93.5% capacity before the Friday atmospheric river storm. By late Friday, the reservoir’s water reached the top of the dam and was flowing over the spillway.

Whale Rock had only spilled 12 other times since its completion in 1961, according to the city. The last time it had spilled was in the 2004-2005 winter season.

“Whale Rock has a relatively small watershed and is fed by creeks, not rivers, which means a much smaller volume of water entering the reservoir during heavy rain events than is seen at larger reservoirs across the state,” the city’s website says.

Droughts have meant the reservoir has typically remained far below the top of its banks.

The last time Whale Rock Reservoir was nearly full was in May 2019 when it reached about 90% capacity, according to the city of San Luis Obispo’s data.

Another reservoir in San Luis Obispo County, Santa Margarita Lake, has been overflowing since early January.

The lake was at almost 111% capacity as of Saturday afternoon, according to data from the San Luis Obispo County Public Works Department.

Lopez Lake had risen to 76% capacity as of Saturday, while Lake Nacimiento was at 83% on Thursday.