A triathlete went to a hospital and about 30 others suffered symptoms of hypothermia Saturday morning during the HITS Napa Valley triathlon in Napa County, a Cal Fire spokeswoman said.
A participant got on a bike after swimming in Lake Berryessa and went down at 10:13 a.m. in the 7600 block of Berryessa Knoxville Road.
Once the bicyclist went down, someone suggested that 30 others stop to warm up.
The triathletes swam in the lake before attempting a bike ride.
The temperature at the lake was 37 degrees, according to Cal Fire.
National Weather Service meteorologist Steve Anderson said the winds were light Saturday morning so wind probably didn't make the air feel any colder.
The participants with symptoms of hypothermia warmed up at the Hope Valley Fire Station and at the Bureau of Reclamation Office. All who warmed up were OK afterwards, Cal Fire spokeswoman Suzie Blankenship said.