A red flag is posted on Jones Beach in Wantagh, New York, in 2021. Howard Schnapp/Newsday RM via Getty Images As with many things, red indicates hazards on the beach.

A purple flag below a red flag in Miami's South Beach. | Dan Lundberg, Flickr // CC BY-SA 2.0. A purple or blue flag indicates the presence of dangerous marine pests, like jellyfish or stingrays.

The latest change adds a double red flag that closes the beaches to all swimming and wading and makes it illegal for anyone to go into the water. Here's what all the flags mean.