Image credit: Courtesy Tony Velardez

As you head to the beach to celebrate the Fourth of July, along with hoards of other Americans taking advantage of the sunny holiday, there's more than just the heat to be cautious of. There have been shark sightings on both coasts, leading to panic in some areas.

Just like a scene out of the movie "Jaws," beach-goers spotted a 14-foot Great White shark off the coast of San Diego on Monday, prompting the immediate closure of the beach. The La Jolla Shores beach re-opened in time for the holiday after there was no sign of the shark overnight.

Area lifeguards told ABC News that while shark sightings are fairly common there, they should be taken seriously.

Another shark was caught just north of La Jolla Shores the same day. A fisherman reeled in what is believed to be a shortfin mako shark 15 miles off the coast of Marina Del Rey.

"It's been at least a couple of years since I've seen anything that big," Tony Velardez, an assistant manager at Del Rey Landing, told ABC Los Angeles affiliate KTLA.

The fisherman said he believed the shark was around 800 pounds - their scales only go up to 750.

And the next day, all the way on the other side of the country, fishermen spotted two more Great Whites off Cape Cod.

And this wasn't the first sighting in that area - a 12- to 15-foot shark was seen over the weekend in Chatham, the state's first of the season.

The town's harbormaster told the Associated Press that Chatham isn't planning to close its beaches for the holiday but that people should be alert and stay close to the shore.

Authorities issued an advisory telling beach-goers to stay away from seals - one of sharks' favorite snacks.

Back over on the West Coast, Lt. Andy Lerum reiterated the advice from Cape Cod authorities.

"Humans are not normal prey for sharks and so every time there is an attack it's assumed it's a mistaken identity, so it's better not to look like a seal if you can avoid it," Lerum told ABC San Diego affiliate 10News.

So enjoy the holiday beach weather, but stay alert if you're planning to cool off in the water on this sweltering July 4.