Some California waterways are still dangerously cold from spring snowmelt, prompting the National Weather Service (NWS) to advise caution amidst an ongoing heat wave.

Excessive heat is plaguing much of the state of California this week, prompting meteorologists to issue a slew of heat-related warnings. However, meteorologists also are advising people to be careful in how they choose to cool off in the hot weather, as area waterways are still cold amid the rising temperatures.

The cold water could be dangerous to people looking to cool off from the heat, particularly over the Fourth of July holiday.

"Heat could significantly impact outdoor holiday activities. Area waterways will continue to run cold and fast, creating dangerous conditions for those seeking relief in rivers and lakes," the NWS office in Sacramento warned.

Meteorologists warned that temperatures could reach up to 115 degrees Fahrenheit in the affected areas. The excessive heat warning is in place for Sacramento Valley, northern San Joaquin Valley, Carquinez Strait and Delta and surrounding foothills.

NWS meteorologist Katrina Hand told Newsweek that some of the rivers and creeks have temperatures as low as in the 60s in that area.

"They're still a bit cold from the snowmelt at the moment," she said. "When we had the really strong winter last year, we had really cold water temperatures going much later in the summer."

The heat wave's impact on the Fourth of July celebrations is also a concern. Authorities advise using only safe and legal fireworks, and to have water sources nearby to prevent any accidental fires.

The combination of high temperatures, low humidity, and strong winds creates critical fire weather conditions. A Red Flag Warning has been issued for parts of the Sacramento Valley and surrounding areas, indicating an increased risk of wildfire ignition and rapid spread.

Local authorities are setting up cooling centers to help residents cope with the heat. Public libraries and other community centers will serve as places where people can find relief from the sweltering conditions. Residents are advised to stay indoors during peak heat hours, wear light clothing, and stay hydrated. Pet owners are also reminded to protect their animals from the heat by providing adequate water and shelter.

"The duration of this heat wave is concerning as the current forecast keeps scorching conditions in place through at least the end of the week," the Weather Prediction Center said in its forecast. The NWS emphasized the danger for individuals without effective cooling and highlighted the increased risk of heat-related illnesses.

With the heat wave expected to persist, Northern Californians are urged to take all necessary precautions to protect themselves and their communities from the extreme weather conditions and the heightened wildfire risk.