If you get to Zanzibar Johnny, try Kizimkazi, it's the southern most tip of the island, pretty deep waters there and you'll have the chance to freedive with dolphins but be careful from all the motorised fishing boats, they take tourists out to snorkel and are darting about all over the place chasing after the dolphins to get the touristas in prime spots, poor dolphins, maybe try a few km away from that point, but not sure what the currents are like, ask locals, was about 8 years ago I was there.....
You based in espana???? I'm looking to do some summer freediving in the med, p.m. me if your interested, I just am looking for a spot with cheap flights and I guess Barcelona ain't bad from the U.K.
Anyway any questions regarding Africa, let me know, i used to live there... For freediving lake malawi takes some beating, can tell you some spots to try.
Ciao!
Paolo