Is there good snorkeling from the beach, or do you have to book an excursion and go elsewhere to snorkle?
I haven't snorkeled there in a couple of years but my neighbor goes to Lagoon 2 in front of building almost every day to swim and snorkel and he says Lagoon 2 is the best place. Apparently there is a turtle that visits the that lagoon on a fairly regular basis.
Aloha! All four Ko Olina man-made lagoons are great and calm for snorkeling, though you really need to snorkel closer to the rocks to see more fish. IF the ocean water is calm enough, in the open ocean, then snorkeling off of Electric Beach (up Farrington Highway a short distance and across from the very obvious power plant on the right-hand side) is a great spot. It's literally a few minute drive from Ko Olina, towards Waianae. Very close. Look at a satellite view on a map and you'll see it. The power plant is called the "Hawaiian Electric Kahe Power Plant" and is right across the street (Farrington Hwy) from the ocean. If you message me I can send you a cool map image that I annotated showing the location of the parking, beach access, water pipe, etc. I'm not able to post links or images in these responses, but I'm happy to email that link to anyone that wants it. It's just a Google Maps satellite image screenshot that I added some annotations to for convenience.
Just be sure to not bring any valuables or leave anything in sight in your car and lock things up. There is a small sandy area there you can snorkel out into the open ocean from. However, if there is wave action I do not advise anyone go from this spot unless you are a strong intermediate or advanced snorkeler or SCUBA diver with experience out in the open ocean. The drowning risk for visitors in the Hawaiian waters are very high, especially for those unfamiliar with the powerful ocean currents. Please keep that in mind.
If you do snorkel out from Electric Beach then go straight out about 1/4 of a mile or so, give or take, towards the patch of moving/rough water. There is an underground/underwater pipe pumping hot water out of the power plant into the ocean. MANY fish congregate at that exit point and it is a popular spot to see fish and sometimes turtles. I've been snorkeling there before and we were lucky enough to be met by a huge pod of 150+ dolphins and we snorkeled with them for quite awhile. Please note, if you snorkel by this water pipe the flow of water is quite strong and if you swim out into that flow you will get pushed pretty far out. Be sure you have good fins and experience and that you are not out there alone. I suggest snorkeling on the inside part of the pipe, meaning before the opening, closer to shore, rather than after the opening as you'll get caught up in the water flow current. If you do get caught in that man-made current then swim perpendicular to it to get out of the flow and only then swim towards shore. If you try to swim against that current you won't make headway and will tire yourself. It's a lot of fun when the conditions are good, just make sure you have fins and a buddy...always.
Beyond that, any other CALM water area off shore that does not have strong currents can make for great snorkeling. Shark's Cove, Hanauma Bay, North Shore Beaches, Waikiki, etc. Ocean conditions are the biggest factor as they vary dramatically with the seasons and depending on the time of year.
Enjoy and be safe out there! Most good snorkel spots do NOT have any lifeguards on duty so keep that in mind.
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