I heard that the water is quite cold around Hawaii. We are planning a cruise to Hawaii in March and where thinking about doing some snorkeling. Not sure to reserve a snorkeling excursion or not. Any answers are greatly appreciated.
I have been to Hawaii many times, several islands, and different times of year. The water has not been cold any of those time. I always take my snorkeling equipment (mask & tube) and go about everyday.
Just rent a car and save on the tour cost unless you just want to stay within walking distance of your hotel. Most islands are easy to drive around.
It wasn't cold any of the 5 places that we snorkeled on 4 islands during our cruise a year ago in January. One place to look at water temperatures: http://www.nodc.noaa.gov/dsdt/cwtg/hawaii.html
My wife and I travel to Hawaii every couple of years and spend every moning snokeling. We have traveled in February, March and June and never found the water cold. Many people rant and rave about Hanoma Bay, but we find it greatly overrated.
There are many great spots on Mauii in the Makena area that can be snokeled from shore. We also love the cruise and snokel to Lanai with Paragon Charters.
On the Big Island you can't beat the County Park just south of Kona. Experienced snorklers also enjoy the City of Refuge off the lava and a trip to Capt. Cook's Monument.