Popular public beaches in St. Lucie, Fla., were forced to close today after sharks were sighted close to shore.

Video taken by St. Lucie County officials showed two sharks swimming in just a couple feet of water.

This follows two shark attacks that happened within about 90 minutes Sunday in Oak Island, N.C., leaving a young girl and teenage boy with severe injuries.

On "America's Newsroom" today, biologist and shark expert Dr. Greg Skomal said that shark attacks are rare, but when they happen, they are very traumatic.

"One of the things we've been trying to do as shark scientists is figure out why these kinds of events occur," Skomal said. "It's very difficult. There's no real answer to these questions. We just look at patterns, we see what's going on and we try to figure it out."

Skomal said that based on the limited information that he has, he believes that either a bull shark or a tiger shark was involved in the attacks Sunday.

"All we can do is try to minimize the interactions by making conscious decisions when we go into the water, realize we're terrestrial animals going into a foreign environment," Skomal said.

Watch more above.

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