Reporter: Just when you thought it was safe to go back in the water some on spring break are saying not so fast. We saw something moving in the water and everybody was saying, ah, shark. Reporter:... See More
Reporter: Just when you thought it was safe to go back in the water some on spring break are saying not so fast. We saw something moving in the water and everybody was saying, ah, shark. Reporter: These pictures show how close these sharks mostly black tipped and spinners are coming to the shore during their annual migration shore. A lot of times when we have a sandbar theystay offshore further. Reporter: They're not uncommon for southern florida beaches. Every year we expect one to come through. Reporter: The migration from florida to north carolina usually starts and ends sooner, well before florida's prime beach season. Not this year. Researchers at florida atlantic university who track the animals say they've now counted some 15,000 sharks, most less than 200 yards from shore. Beauty of living in florida, also danger. Reporter: As a precaution, this morning many beaches are on high alert with double red flags waving keeping vacationing swimmers out of the water for now. The sharks are not to be reckonith and people need to heed these warnings. Black tipped sharks only account for 20% of un provoprovoked attacks in florida. This morning people respect taking any chances. For "good morning america," john muller, abc news, new york.
This transcript has been automatically generated and may not be 100% accurate.