Last week, the day after I returned from the Sea of Cortez, I agreed to meet a friend for an afternoon swim. When the hour arrived, though, I didn't want to go. Having spent the last two months in and on the ocean, I felt water-logged, jet-lagged and pressed for time. Being too late to renege, though, I donned mask and snorkel and plunged in.

And something amazing happened. Underwater Hawaii looked as good to me as the first time I saw it at Hanauma Bay in 1982 when I fell in love with the ocean.

The water off Lanikai Beach was so warm and clear I felt I floated on air. The coral heads seemed almost loving as they cradled fish in their curvy arms. And the color—the corals' pinks, greens and blues looked like paint on palettes. The scene was so enchanting I wouldn't have been surprised if the fish called out, “;Aloha!”; as I swam by.

Some snorkeling excursions are better than others, of course, but this wasn't just a particularly good day. Hawaii's waters dazzled me so because I had been swimming where the water is chilly and green and the reefs are rocky and brown. That's not bad. Just different.

The water in the Sea of Cortez, also known as the Gulf of California, is murky because of upwelling, a term in oceanography meaning water rising from the ocean depths. Because dead plants and animals sink, deep water is rich with their remains. Rotting tissue might not sound particularly appetizing, but it's a holiday feast to marine life. The nitrogen and phosphorus in this material are fundamental ingredients of fertilizer.

This fertilizer gets to the top in the gulf because of its large tides and strong winds. In the north, tides range up to 30 feet, and during my last trip, a surprise northerly blasted us with wind we clocked at 43 mph.

The result of these forces is currents that scare me just reading the charts. One channel is called Canal de Salsipuedes, “;leave-it-if-you-can channel.”; Another is Canal de Infiernillo, “;little hell channel.”;

Such strong currents move a lot of surface water and that allows deep water to rise.

Besides being full of fertilizer, deep water is also cold, and, therefore, high in oxygen since cold water holds more oxygen than warm water.

Add this oxygen to abundant fertilizer, stir in long hours of desert sunlight, and you have a recipe for the bountiful marine life famous in this gulf. John Steinbeck described the Sea of Cortez as “;ferocious with life”; and when I'm there, that fitting phrase often comes to mind.

Hawaii, on the other hand, has a small tidal range and our trade winds don't move enough surface water to give deep water a chance to rise. Our waters are, therefore, warm, clear and low in nutrients.

But just because we're surrounded by a marine desert doesn't mean it's lifeless. Stony corals love warm, clear water, and the reefs they build here provide oases for extraordinary numbers of marine animals needing food and shelter.

They also give us color. Corals use their stinging tentacles to catch passing animal plankton, but get their veggies by hosting algae in their tissues. It's these tiny plants that give corals their vibrant colors.

Among the charms of snorkeling for me is the anticipation of seeing something remarkable. Big score this time. I saw why I love being home.

Susan Scott can be reached at www.susanscott.net.