Beaches on South Florida's Atlantic coast were closed again Friday after sightings of thousands of migrating sharks, authorities said. Many tourists expressed disappointment that they had to stay out of the water. The sharks were seen along the coastline, heading back north after migrating south for the winter, marine biologists said. Lifeguards at Midtown Beach in the Palm Beach area saw spinner sharks and raised red flags, indicating swimmers should not enter the water, NBC News reported. "It's dangerous. It's not what you would expect. Families come out here to enjoy the weather, beach and sand, but now they can't," said beachgoer Guirlene Exantus. "We don't have sharks in Washington. I just wanted to go swimming," said Tori Bradshaw, who had just arrived in Florida from her home state. "If there are sharks, you aren't going to find me in there," said Burt Abrams, visiting from Cleveland. Swimmers were advised to swim close to shore at beaches that remained open with lifeguards, and to remove jewelry before entering the water because sharks can be attracted by silver, yellow and gold colors, NBC said.