Stoked on coming to Hawaii, I live on Oahu and Freedive here all the time
Oahu:Hanauma Bay, go early, know it’s closed on Tuesdays and be prepared for a 10 minute video before entering the park. Depending on your skill level and waves you can go beyond the buoys and see way more fish and other marine life.
Electric Beach or Kahe Beach park: my personal favorite, about a 150 yard swim to two giant water outlets that blast warm water from the local trash burning power plant. Tons of fish swarm this area, turtles, occasional white tip reef shark (rare), rays and dolphins (go at 7am for best results)
Makua bay also called Pray For Sex - far west side of the island, good for shells and amazing backdrops. Dolphins early morning but a long drive from Waikiki (1.5 hours)
feeling adventurous? I suggest One Ocean Diving for a shark tour, just a mindblowing experience and very safe.
Maui: Molokini crater is the bomb -just go.
Big Island: 2 step Beach is awesome - watch out for Vana aka Sea Urchins
Do a manta night snorkel - you wont regret it.
As with everywhere in Hawaii, don’t leave anything of value in your car, it will get stolen. Don’t leave anything on the beach either, get a personal water proof bag or case and keep it with you.
Any questions - drop me a message.
mahalo!
Bret