Whether you live near a beach or you’re heading to the shore this summer, you’ll likely notice different colored flags displayed high above the sand. For example, do you know what a purple flag means?

Purple beach flags indicate dangerous marine animals in the water. That could include jellyfish, stingrays, and potentially harmful fish.

The last thing you want is to recreate a scene from Jaws while you’re on vacation, so paying attention to these flags is important! Before you step into the water, they can alert you to any potential hazards you could face while swimming.

Seeing a purple flag doesn’t necessarily mean you have to stay out of the water. But, you should exercise caution if you decide to take a dip and consider keeping small children out until the flag is removed. But honestly, do you really want to take your chances in a battle with a jellyfish?

It’s also a good rule of thumb to remember what some of the other flags mean when you’re at the beach with the family.

A red flag means there are strong currents and you should avoid the water. Yellow indicates “medium hazardous” conditions, and green means calm conditions, though you should still exercise caution at all times.

Going to the beach should be a fun and relaxing experience, but it also needs to be a safe beach trip for the whole family. Even if the water seems calm and the waves are lazy, don’t assume it’s a good idea to go in the water.

Pay attention to all flag colors—including purple—the next time you’re at the beach, and you’ll enjoy peace of mind when you step into the water.