Just off the coast of Nyali and Mombasa beaches you'll find the Mombasa Marine Reserve: 200 sq km of fish, rays and coral fringe reefs that are a favorite of travelers more so for their proximity to the city than for any superior diving or snorkeling conditions. Water temps here are warm but not tropical, usually hovering somewhere in the mid to upper 70's (F), and the visibility at a depth of 20 meters is adequate enough to enjoy the show.
Not convinced? We can probably sweeten the pot a little better than that. With over 15 sites at its disposal, the Mombasa Reserve offers a variety of cool destinations for novice divers to explore, including Shark Point and the Brain Coral Gardens, along with advanced-only sites like The Wall and The Wreck. Marine life here runs the gamut from urchins and groupers to reef sharks and sea turtles, so no matter where you're submerged you're bound to find plenty of activity. Suffice to say, as long as your expectations are grounded, you'll be hard pressed to find a more ideally situated destination for satisfying that urge to get below the surface and explore the Indian Ocean.