There is always a risk for shark attacks in Cancun or any other place near the ocean. Even though sharks love tropical places, there is only two registered attacks that occurred on the beaches of Cancun in the last 10 years. Whenever you decide to swim in the ocean remember to stay close to the beach and leave the wild life alone, sharks and most of wild species need a reason to attack people. If you listen to the lifeguards recommendations and  use your common sense you have a very low possibility of being attacked by a shark in Cancun.