Gulf of California is a marine treasure

From the Colorado River delta in the north to the tip of land on the Baja peninsula, where it joins the Pacific Ocean, the waters of the Gulf of California are so rich in microscopic life called plankton that they turn the sea vermilion at times.

Surrounded by desert mountains, 100 islands and pinnacles in the Sea of Cortez (as the Gulf of California is also known) support a variety of animals and plants.

The sea contains a richness of life that lures divers and scientists to these waters to study and observe blue whales, the largest creatures on earth, and whale sharks, the largest fish in the oceans.

Small colorful invertebrates, thought to be rare in other places, abound in the waters between Mexico's mainland and the peninsula of land that extends almost 1,000 miles from Tijuana to Cabo San Lucas.

When Tim Means came to the Baja from Arizona in the mid–1960s, he was so taken by the beauty and remoteness of the place that he stayed.

He formed a company called Baja Expeditions and took visitors on trips to explore rock art that Getty Foundation researchers dated as approximately 1,000 to 1,500 years old.

Enthralled by the size of the fish and marine mammals in the sea, "I decided to reconstruct a boat to run dive trips," he says. "There are big groupers, big mantas, big sharks, whale sharks, and many species of whales."

There is no better way to explore the underwater environment and islands in the Sea of Cortez than by boat. While other dive boats take day trips out of La Paz, leaving at 7 a.m. and returning at 6 p.m., Mr. Means's 80–foot live-aboard vessel, the Don Jose, takes week-long excursions and visits remote islands.

The islands and pinnacles are small, but, like icebergs, their volume is far greater underwater. Las Animas has a small horseshoe bay that offers protected anchorage. Pangas – outboard-powered launches towed by the Don Jose – take divers around the island to pinnacles where schools of jacks, tuna, and large groupers swim with seals and sea turtles.

The rocks around Las Animas sport a variety of nudibranch not often found in one place. Nudibranchs are mollusks without shells. Their bright colors and frilly gills warn fish that they are not tasty. Yellowtail surgeon fish and odd-looking striped hawkfish are everywhere. There is even a chance to see the timid scalloped hammerhead shark.

The rocky islands of Los Islotes are home to a permanent colony of California sea lions. Early summer is mating season, when the large males are protective of their harems.

Later, the rocks are home to mothers and little pups, who – along with frigate birds, brown pelicans, boobies, and rare Heermanns gulls – offer wonderful visual opportunities to photographers and naturalists.

Divers can enjoy cavorting sea lion pups as well as a lone elephant seal, which swims 400 miles from its normal home on the coast to enjoy the company of Los Islotes sea lions. The crew of the Don Jose cannot say why, only that it returns every year and sometimes greets divers with a friendly hug.

The merging of currents and mingling of warm and cold water off the large island of Espiritu Santo and its neighboring chunk of rock, Isla Partida, attract large sea creatures.

Hundreds of dolphins cavort near the bow of the Don Jose. Pilot whales breach and sound underwater. Around a sea mount called El Bajito, young sea lions play with the anchor line, trying to untie the knotted rope.

South of La Paz is the island of Cerralvo. A solitary rock in the middle of the channel with a light tower is called Roca La Reyna. A small family of sea lions lounges on the rock, which can be approached only in calm seas.

Underwater, rays and scorpion fish abound, as do large groupers and schools of green jacks and small Creole fish so numerous that swimming below them gives the impression of a large cloud passing overhead.

Gorgonian sea fans grow on the rocks as colorful backdrops to underwater settings where there are so many different species of fish and marine invertebrates that it is hard to focus on just one.

Once below the thermocline, which varies from near the surface to 60 feet below, the Sea of Cortez is cold. Wetsuits and hoods are comfortable, and hot soup aboard the Don Jose is welcome after diving.

After all that exertion, divers are delighted to be served generous meals: Shrimp served over rice, corn, a fresh vegetable salad, broiled fish, or even T–bone steaks provide the fare at dinner. Lunches feature tacos, enchiladas, fish, and salads. Fresh fruit and sweets are always available.

There are few places left in the world where visitors can enjoy unspoiled wilderness. In Baja California there are still discoveries to be made. The sea is so vast that many spots are virgin areas that divers enjoy for the first time.

"It's a wonderful place," Means says. "It would be a shame to let it get away from us with huge hotels on every beach. It is going to take a joint effort by government, the scientific community, commercial interests, but especially government, to protect and preserve this environment.

"I hope that people come away from their trip here with some understanding of the valuable natural sites they have visited and will help keep them valuable by the way they live or by changing the way they live."

• For more information, contact Baja Expeditions at 2625 Garnet Avenue, San Diego, CA 92109. Phone 800-843-6967, e-mail travel@bajaex.com, or visit the website at www.bajaex.com.