A dangerous heat wave is expected to drive Americans to the coast in search of relief this week but millions of beachgoers are being told to avoid the ocean because of elevated bacteria levels.Public health officials have warned beachgoers in California to avoid entering the water at several Los Angeles County beaches because of the issue, which could increase the risk of illness.Meteorologists said last week that most of America’s Lower 48 states would endure an "unusually large, strong and long-lasting" heat dome with "significant and dangerous" temperatures.The severe heatwave, with temperatures 15 to 25 degrees Fahrenheit (8 to 14 degrees Celsius) above normal, began this weekend and is expected to persist for at least a week, with some regions experiencing its effects through the end of the month.The severe heatwave with temperatures 15 to 25 degrees Fahrenheit (8 to 14 degrees Celsius) above normal began this weekend and is expected to persist for at least a week (NOAA)Temperatures across Southern California are expected to climb through midweek, with some inland communities forecast to exceed 100 degrees and beach communities expected to see highs in the 80s and 90s.Forecasters are specifically concerned about elevated nighttime temperatures, which pose a particular threat to human health."Nights can be just as dangerous as days. If you don’t get heat relief at night, that’s going to spill out into your daytime experience and become extremely dangerous," warned Bob Henson, a meteorologist with Yale Climate Connections."Heat is not to be played with,” he continued. “It’s just as dangerous as a tornado or hurricane that can kill you just as easily, just in a quiet and different way."The Los Angeles County Department of Public Health issued ocean water warnings for the following locations:Bel Air Bay Club storm drain at Will Rogers State Beach, 100 yards up and down the coast from the club border fence;Solstice Creek at Dan Blocker County Beach, entire swim area;Mother's Beach in Marina del Rey, entire swim area;Inner Cabrillo Beach in San Pedro, entire swim area;Castlerock storm drain at Topanga County Beach, 100 yards up and down the coast from the storm drain;Topanga Canyon Beach in Malibu, 100 yards up and down the coast from the lagoon; andSanta Monica Pier, 100 yards up and down the coast from the pier.The alerts were issued after recent water samples showed bacteria levels exceeding state health standards, which could increase the risk of illness for swimmers, surfers and others entering the water.Public health officials have urged residents to stay hydrated, limit outdoor activities during the hottest part of the day, wear lightweight and light-colored clothing and seek air-conditioned spaces if their homes become too warm. Officials also reminded residents never to leave children or pets unattended in vehicles, even for a short time.