SAN DIEGO • The last time I saw the Yukon, a 366-foot-long Canadian Navy destroyer, it was docked in San Diego. So many holes had been cut in the sides of this well-worn vessel that it reminded me of a big hunk of Swiss cheese.

That was a little more than a decade ago, and volunteer crews were gutting and cleaning the ship, preparing to scuttle it to create an artificial reef in 105 feet of water two miles off Mission Bay.

Since then, I’ve wanted to visit the ship in its sandy resting spot, but the birth of two children and a move back to the Midwest got in the way.

I finally got my chance this past summer during a visit to San Diego, where I’d lived from 1999 to 2003.

On a sunny July morning, I found myself floating on the Humboldt dive boat, listening to captain Ryan Wilbarger as he briefed St. Louisan Jim Koetting, me and a half-dozen other divers about what we would find on the ship. He also warned us, in no uncertain terms, not to enter the Yukon unless we had training in technical diving.

For Koetting, a photographer and author who works in the financial services industry, it was his second visit to the Yukon, following a warm-up dive last December.

“I had to come back,” Koetting told me. “Wrecks are pretty amazing in themselves, and the red-and-orange soft coral polyps growing all over the ship are pretty cool, too.

“I’ve dived in a number of Missouri lakes, the Florida Keys and the Bahamas, but the cold-water corals are a lot brighter,” he added.

Then, warm and toasty in a thick wetsuit to ward off the chill of 50-degree water we would find in the depths, I jumped in.

SAN DIEGO’S ‘WRECK ALLEY’

Several feet away from me floated Virginia Hatter, a scuba instructor and my guide for a day of diving on the Yukon and the nearby Ruby E, a 165-foot Coast Guard cutter sunk in 1989 in about 90 feet of water.

The ships are two of six vessels that make up San Diego’s “Wreck Alley,” about two miles off the coast and one of the West Coast’s premier dive spots. Other wrecks in the so-called alley include a 95-foot-long kelp cutter and a 100-foot-tall Navy research tower that was knocked over by a powerful El Niño storm in 1988. Many of the wrecks are covered by strawberry and yellow anemones, purple and brown gorgonians, hydrocorals, mussels, sponges and sea urchins.

Because I hadn’t dived in more than a year — and because the Yukon is a challenging outing in potentially strong currents — I’d warmed up the day before with a relatively shallow dive.

I chose the cove at the southern end of La Jolla Ecological Reserve to check out the kelp and look for sevengill sharks with instructor Nick Le Beouf, who works for the OEX dive and kayak shop in La Jolla.

We weren’t disappointed in our search for the sevengills. During our 45-minute meander, we encountered five of them, including one that was close enough for Le Beouf to touch.

Though we also saw bright orange Garibaldis (which look like giant goldfish), crabs, starfish, lobster and a variety of fish, the best part was swimming through the translucent kelp, which waved each time the ocean surged.

And even though I know the chances of meeting up with a great white shark are relatively small, I couldn’t help but think about an unlucky chap named Robert Pamperin.

He was free-diving (snorkeling) with a friend about 50 yards offshore in the cove when he was attacked in 1959 by what witnesses and his friend described as a huge, 20-foot-long great white.

The shark struck from below and lifted Pamperin, 33, up out of the water as his girlfriend watched from the shore. The shark held him upright momentarily before submerging and thrashing Pamperin in his jaws.

‘THEY GET A BAD RAP’

A search for Pamperin was unsuccessful. Only a swim fin was recovered, and some reports described the swimmer as being swallowed whole, feet first.

“Great whites can certainly be dangerous, but they get a bad rap,” said Le Beouf, a former whitewater rafting guide who leads shark-viewing trips (inside cages with thick bars) off Baja California.

And while I was glad that we got to see several sevengills — who seemed to be afraid of us — I have to admit I was worried about running into a great white.

Le Beouf and I spent most of our time in the cove, where I had dived a decade ago, at less than 40 feet. So I was still a bit nervous the next day when it came time to descend 100 feet to the Yukon.

“A little nervousness is good,” Hatter had told me on the Humboldt deck as we checked out our gear and made sure we had plenty of air before our first swim. “You never want to be cocky about diving.”

At a buoy marking the bright gold line that descended to the deck of the Yukon, Hatter gave me an energetic OK sign as we let the air out of our buoyancy compensation vests and began to drop.

I cleared my ears repeatedly as I slid slowly down the line, keeping my eye on the blinking strobe light she had clipped to her vest. Visibility was about 25 feet that day, but the water became green and dark the deeper we dropped and — truth be told — a little creepy.

After we descended for several minutes, the outlines of the ship’s superstructure came into view, then the bow, a ladder, a round window and gun turrets. One of the first things I noticed when I got up close were foot-tall, flowerlike white giant plumose anemones that were blooming all over the Yukon.

On closer inspection, I could also see that a carpet of red, pink, purple-orange and red club-tipped anemones covered the hull. A brilliant blue and gold nudibranch stood out from the other, more subtle colors. Over the last decade, the Yukon had changed from a rusting hulk into an undersea garden, thanks to cold, nutrient-rich currents.

Because the ship tipped on its port side when it sank, the deck had become a 40-foot wall, with its towers and gear facing west. As we swam along the 90-degree deck, we saw sheepshead, rockfish, cabazon, goby, blacksmith, surf perch and a large crab hiding in a ladder.

DANGEROUS CURRENT

On another spot, wavy kelp slurped in and out of a hole in the deck with the gentle surge. When the current is stronger, I was warned, divers can be sucked into the hull and then spit out. I gave the hole a wide berth.

After 20 minutes, we began a slow ascent, pausing several times for safety stops to let nitrogen bubbles escape our blood. Back on board the Humboldt, we warmed up with hot tea, soup and salad.

An hour later, we were back on the Yukon. I poked my head inside the hull and was tempted to enter. But caution — and fear of a scolding — kept me outside. Then we swam forward to check out the gun turrets and big cutouts in the shape of dolphins in the bow.

The warning about entering the Yukon’s bowels is no idle threat. We swam by a plaque dedicated to veteran diver Steven Donathan, who discovered a B-36 bomber that crashed off San Diego in 1952. He found it in 2004 at a depth of 267 feet and led a History Channel camera crew to the location for a program.

But Donathan, who was also a technical diving instructor, died in 2005 on the Yukon when he entered a boiler room that had been welded shut and apparently was unable to get out. Some in the diving community criticized Donathan for breaking basic safety rules because he didn’t mark his route with a guide line. Others suggested his death was a suicide. For many San Diego divers, he remains something of an icon.

Back on deck after our second Yukon dive, I shivered before warming up again with more hot tea and tasty soup.

For the last dive of the day, we descended to the Ruby E Coast Guard cutter that is beginning to crumble after nearly 25 years underwater.

Because pieces of the interior were deteriorating, we were warned to stay out.

“Your air bubbles could lift the ceiling of a room,” the Humboldt’s captain warned. “Then when the bubbles escape, that ceiling could collapse on you and trap you.”

So I was more than happy to drift along the outside of the ship. And to my eye, it was more colorful and heavily forested with anemones and other sea critters than the Yukon.

Better yet, it has an even more interesting story than that of the Yukon, which was launched in 1961 from North Vancouver, British Columbia, and had a relatively uneventful career.

The Ruby E, however, was built in Seattle during Prohibition and designed to catch rumrunners bringing in hooch from Canada.

It patrolled Alaskan waters for submarines during World War II, was decommissioned in 1950 and ended its career, so the stories go, ferrying drugs from Mexico to California.