Bora Bora does contain many sharks so you need to be very careful if you swim in the waters in Bora Bora.
The Bora Bora island is surrounded by A barrier reef and also has many other wild marine life besides sharks.
Bora Bora also has sting rays and barracudas as well so when swimming in the waters there you should be very careful and cautious and if you do see a shark, sting ray etc then get out of the water right away until the shark or stingray or other marine life has gone away.
Many people do safely swim in the waters in Bora Bora so just use caution and you should be safe.