Those heading to the beach this week are advised to stay out of the water as several beaches are under advisory for excessive bacteria levels on Thursday.

Seven beach areas have been placed under warnings for high bacteria levels by the Los Angeles County Public Health Department and the OC Health Care Agency.

These areas are under advisory, which means the “ocean’s water bacteria levels exceed state standards and may cause illness.” Those with weakened immune systems, along with children and the elderly, are most at risk officials said.

Los Angeles County beach areas affected by the warnings:

  • 8th Street extension in Manhattan Beach
  • White Point at Royal Palms Beach
  • Redondo Beach at Sapphire St.
  • Castlerock Storm Drain at Topanga County Beach
  • Malaga Cove in Palos Verdes Estates
  • Santa Monica Pier in Santa Monica
  • Mother’s Beach in Marina Del Rey

Orange County beaches affected:

  • Poche Creek at Poche County Beach in San Clemente
  • Pico Drain at North Beach in San Clemente
  • Capistrano Bay Community Beach in Dana Point

The closure of Topanga Canyon Beach in Malibu earlier this week was lifted on Thursday after recent samples “identified water quality levels within state standards.”

The exact cause of the heightened bacteria is not known, but officials say runoffs from rainstorms can also contaminate waters. If heavy rainfall occurs, it’s typically advised to stay out of ocean waters, rivers, creeks or flowing drains for at least three days after a storm.

Interactive maps on the L.A. Public Health Department site and the O.C. Health Care Agency site offer the most current beach warnings and closures.

Ocean water samples are tested every week throughout the year to ensure the bacteria levels remain within state-accepted standards.