Surfing legend Laird Hamilton has some simple, and possibly controversial, shark advice -- if you're a woman and you're on your period, stay outta the water ... 'cause you're gonna get bit.

We got Laird in Malibu, naturally, and asked him about the rash of shark sightings on SoCal beaches lately. He downplayed the danger ... well, unless you're a woman.

Look, Laird's like the closest thing to a real-life Aquaman -- it's rare to catch him on land -- so he qualifies as an expert on water activities. He also did NOT seem to be kidding about these tips for avoiding sharks.

Orange County Sheriff's Department

That being said ... we can't find any scientific studies to back up some of what he's saying here. So, you might wanna take it with a grain of sea salt.

On the other hand ...