LOS ANGELES — Police in Santa Barbara launched an investigation this week after more than two dozen half-marathon runners showed up at hospitals with “unusual symptoms” after participating in a race on Sunday.

The roughly 6,000 people who participated in the half-marathon and 5K were running in temperatures that were much warmer than usual for Santa Barbara, known for its ocean breeze and mild Mediterranean climate, and with little respite from the sun. It reached 86 degrees at noon, compared to a typical high of 71 degrees, according to the National Weather Service.

While the race organizer confirmed they treated runners for dehydration and overheating, some online have speculated that something more sinister could be the cause the illnesses.

Police have not yet determined exactly what landed 27 people in two Cottage Health emergency rooms in Santa Barbara and Goleta, but said in a statement it is “actively investigating these reports.” The Santa Barbara Police Department did not provide additional comment.

On Sunday, officials reported that 19 people who had participated in the race, sponsored by the popular running shoe brand Hoka and organized by the group Run Local, were hospitalized. But, by Monday, that number had grown to 27.

Three people who participated in the race remain hospitalized in stable condition. The rest were released after receiving treatment, Cottage Health spokesperson Cristina Cortez said in a statement.

The race’s local event director, David Monico, said multiple people suffered from heat-related issues.

“Our medical team treated numerous runners for dehydration and overheating both on the course and at the finish line,” Monico said in an emailed statement. “Some of those runners were transported to local hospitals for further treatment and enhanced care.”

Monico declined to comment on rumors circulating online that someone may have contaminated water stations along the race course. Participants said they believe the heat was to blame for the rash of hospitalizations.

Kate Sheppard, 38, said she prepared for the forecasted heat Sunday days in advance, drinking above her normal water and electrolyte intake to saturate her body with fluids. She knew the sun would be out and that temperatures would be higher than normal, she said.

The course keeps runners along the water for most of the race, but near the end, leads them up a steep hill, she said.

“You’re in unrelenting sun along the beach for most of the race, and there’s just no shade,” Sheppard, a private yoga teacher in Los Angeles, said. “That was really tough and mentally tough.”

It would have been particularly difficult for those who took the longest to finish the race, she said, because temperatures climbed as the day progressed.

Sheppard and two other runners who spoke with The Times said they drank at every water station and did not fall ill.

Ian Varley, 75, said he stopped to drink at every station but did not fall ill, though he saw one woman vomiting. Varley, who is from Irvine and has run more than 100 half-marathons, said the race was “beautiful.”

Patrick Tatum, 32, has run the Santa Barbara half-marathon seven out of the last nine years. In the past, a thick marine layer helped protect runners from the sun, he said. Not so this year.

As an experienced runner, Tatum said he knows to prepare by wearing sunscreen, drinking water early and often and not overexerting himself at the outset. People with less experience might not all know to do those things, potentially leading to problems, he said.

Tatum, a personal trainer in Santa Barbara, said he saw an ambulance and a few people in the last mile of the race who appeared dizzy.

“As you were running, the heat was increasing,” Tatum said. “So you’re getting more tired, and the heat’s going up.”

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