The only way to get to the Coronado Islands is by boat, you can dive there, but as they are in Mexico, you can't dock and fishing requires a Mexican fishing license. There are a number of dive boats that leave from San Diego every day of the week, check out Ron Fuller's web site for some of the best. Boats leave from all over San Diego and take between 50 and 90 minutes to get there. Once there, the boat operators know all of the really good sites (and they vary greatly due to wind and swell conditions), so you just put on your gear and go. It is to far to take our Zodiac style boats to.
Boat dependent and they vary greatly, ask.
I like boat diving, it seems so civilized to just gear up, jump in, swim around, and clamber out. The best of all entries.
Being in Mexican waters, the Coronados are pretty well fished out and sit in the open ocean. This means that there is not a lot of life and not a lot of kelp. But you can count on 70-90 foot vis, friendly Seals, Sea Lions, 20 tentacled Sun Stars, Sea Slugs, Abalone, Brittle Stars, Moray Eels, and open reefs. Doesn't sound so bad put that way, does it? Just don't look for Lobster, they have all gone to better places by way of the restaurants of Rosarito.
This is about as close to pelagic diving as you can get to in 2 hours. The three Islands of the Coronados are just barren peaks jutting out of the water (look for the non-native mountain sheep!!) and the underwater area look much the same. Lots of big boulders, long sections of reefs, lots of hidey holes for eels and fishes. Sites to check out are Pukey Point (on the north side of North Coronado), Lobster Shack (same island east side), the Keyhole (just south of Lobster Shack), and the Coronados Ridge (between Middle and South Coronado). Depths at all of these site range between 50-110 feet.
In a word, clear. Visibility is always 50-70 foot better in the Coronados than locally. However the temperature tends to drop a bit to, expect 52-62 degrees (season dependent), so bundle up and wear your hood and gloves, just like mom told you too!
Strong currents, especially at the Keyhole. Your dive master will give you a pre-dive briefing that will summarize the currents for the location you are diving. The water is very clear, you can easily see the boat from 70 feet.