Locals are warning of whirlpools in the lake where Naya Rivera died, though authorities say it's unlikely. Here's how whirlpools form.

• Actress Naya Rivera died of an accidental drowning at Lake Piru, California, local authorities determined on Monday.
• The lake is known for strong afternoon winds and cold water temperatures, which create difficult conditions for swimmers.
• A Change.org petition suggested that dangerous whirlpools could be responsible for some deaths there, but authorities said that's unlikely.
• Whirlpools form when two opposing currents meet.

Authorities recovered the body of 33-year-old actress Naya Rivera from California's Lake Piru on Monday. She is believed to have drowned on July 8 during an outing with her 4-year-old son.

Rivera's son told authorities last week that he and his mother were swimming in the lake before the accident. Rivera helped him back onto the pontoon boat they had rented, but when he looked back, he saw her disappear under the water. An adult life vest on the boat suggested that Rivera had been swimming without a flotation device.

"She mustered enough energy to get her son back onto the boat, but not enough to save herself," Ventura County Sheriff Bill Ayub said during a Monday news conference.

Lake Piru is known for its strong afternoon winds and cold water temperatures — which is why authorities recommend that swimmers wear life vests. Roughly a dozen people are presumed to have drowned there since 1994.

A recent Change.org petition created by Ventura County locals called for officials to erect warning signs about the hazards of swimming in the lake.

"Naya Rivera is not the first, nor the last to go missing at Lake Piru," petition organizer Erin Jordan wrote. "Lake Piru is a very deep lake with very bad whirlpools."

But Captain Eric Buschow, the communications officer for the Ventura County Sheriff's Office, told Business Insider that the chances of a whirlpool forming on the lake were slim.

"I've never heard of a whirlpool there," he said. "There are some currents and there's wind and things like that."

In order for a whirlpool to appear, he added, "you'd have to have a lot of water flowing."

Here's the science behind that process — and what makes a whirlpool deadly.

Like pulling the plug in a bathtub

Whirlpools form when two opposing currents meet, causing water to rotate (like stirring liquid in a glass). This can happen when heavy winds cause water to travel in different directions. As the water circles, it gets funneled into a small cavity in the center, creating a vortex.

Many whirlpools aren't very big, so swimmers can resist the force pulling them down. But whirlpools can also move through open water, forcing swimmers to outrun them. The process can be exhausting, even for an experienced swimmer.

Other whirlpools are large enough to suck people in.

In June 2015, a giant whirlpool formed in Lake Texoma, which sits along the Texas-Oklahoma border. The lake had overflowed that year after several weeks of heavy rain, so local officials decided to drain the water by opening the Denison Dam. The result was like pulling the plug in a bathtub: as the water grew shallower, it started to swirl.

The ensuing vortex was 8 feet wide — enough to swallow a boat.

A history of sudden deaths on Lake Piru

Robert Inglis, who assisted in the search mission to recover Rivera's body, told CBS LA on Friday that the dam connected to Lake Piru — the Santa Felicia Dam — creates a current in the lake. According to the California Water Board, water is retained and stored in Lake Piru during the winter and spring. It's then released from the Santa Felicia Dam in September and October at an average rate of 270 cubic feet per second.

Buschow said the United Water Conservation District plans to lower the lake level in August.

But he added that authorities don't think Rivera's death had any connection to whirlpools or the nearby dam. The dam is on the south side of the lake, he said, and surveillance footage shows that Rivera rented a boat on the north side, which is also where her body was found.

"We think what happened was the boat was not anchored and they were swimming and probably the boat started to get away from her," Buschow said. "In the afternoon, it gets pretty choppy on the water."

Still, other deaths on Lake Piru have involved people seemingly swallowed up by open water.

In 1994, a 27-year-old man was pulled under the water while wearing a life jacket. His body was found on the shore five days later. Three years after that, a man dove into the water to save his daughter. The girl survived, but the father never resurfaced.