The anchorage on Koro is a resort anchorage, and you need to pick up one of their moorings so you don’t damage the reef. Call on the radio. If you don’t get an answer, just pick up a mooring ball. (I’m not sure what you’re supposed to do if none is available.)
Koro is actually sort of a real estate development, and the “resort” is actually a place for people to stay who are looking at buying a place here; so there’s not much in the way of services. They do serve happy hour drinks, and they do make dinner and you can reserve and partake. Don’t expect resort-level food. It’s decent, and I’ll leave it at that. It is a lot of fun to go have evening drinks as some of the people who’ve bought places come down to enjoy the place and they are some nice folks (I’m over 50 so I can use words like folks).
As far as the diving and snorkeling, it’s magnificent! But you have to know where to go. We’ll try to do a post on it, but you can get general directions a couple of good spots in Soggy Paws (it’s north of Nanavuca rock in the middle of the bay).
(No Sevusevu, but you can walk a couple of miles to a village and do one there if you’re into it.)
Update 2018: Sadly, it seems, Koro Island was right in the path of Cyclone Winston (2016) and was hit hard. We’ve heard the homes were destroyed but are being rebuilt. I don’t know how the reef fared, but I fear it’s probably been damaged.
Where’s Legacy (Koro edition)
Koro Island
Koro Island Day Two