For once, I am at the right place at the right time. The bow of the dive boat Northwind slices through the mirror-smooth waters of Lake Ontario, fragmenting the reflection of the cloudless blue sky."The nicest day in at least a month," observes boat captain and shop owner Cliff Rowe. "We've had a lot of rain and rough weather. Still, our boats were full most every weekend."There are a number of reasons why divers from as far away as Michigan and the Carolinas travel to Limestone Dive Center in Kingston, Ontario. We were about to drop overboard and visit one of these reasons."Five minutes to the wreck," Cliff calls.I zip up my dry suit and wriggle into my OMS double tanks. Across the deck, three divers from Toronto don wetsuits and single tanks. They are actually better suited for today's dive profile, which calls for a dive to 100 feet in water that is 71 degrees on the surface and perhaps 60 degrees at depth.My choice of gear was based on a pre-trip misconception: I didn't realize how easy summertime wreck diving in Lake Ontario could be. We make giant-stride entries off the stern and swim to the mooring line. There is a slight hint of current, and visibility is down in the 30-foot range, thanks to a summer algae bloom.A fixed yellow line leads down into unseen depths. As my gauge registers 70 feet, a shadowy outline takes shape from the green gloom. Ten feet deeper, the water temperature abruptly drops a dozen degrees and visibility doubles. Suddenly, we can make out the massive timbers and gears of the Munson.Before the dive, I brushed up on the history of this wreck by reading Cris Kohl's book Treacherous Waters: Kingston's Shipwrecks. As a result, I know that I am looking not at a ship, but rather a large steam-powered dredge that sank while being towed to a job site. No lives were lost when the Munson abruptly took on water and settled into a deep channel near Amherst Island, but the crew had no time to salvage any tools or machinery.At 85 feet, I am suspended above the dredge's upper deck, with a clear view of its intact steam engine and boilers. Swimming forward past a clump of upright pilings, I encounter the jaw of the massive steam shovel, which bears a light coating of zebra mussels.These non-native bivalves first hitchhiked their way into the Great Lakes in the early 1990s, living in the bilge water of ocean-going ships, then took root in their new environment with tremendous enthusiasm. Within a few years, zebra mussels coated everything from dock pilings to water pipes, causing tremendous problems for boaters and marine businesses. The zebra mussel invasion has proved a mixed blessing for divers. On the one hand, these organisms coated many iron and wooden wrecks with thick living carpets. On the other, the filtering power of these small mollusks has significantly improved water clarity. Sites that routinely offered 10-foot visibility a decade ago now boast 50 feet or better, and can approach 100 feet at certain times of year.Because the Munson rests in a deep channel, where there is minimal current, its superstructure has relatively few mussels. I can clearly see grain patterns on some of the upper deck's wooden beams.Near the stern, divers have assembled a display of porcelain plates and enameled bowls collected from in and around the wreck. I take my turn admiring these bits of submerged history, then drop through an opening into the shadowed space between decks. Here, lingcod thread their way through a bewildering collection of chains and gears, and iron hand tools lie scattered about the deck as if abandoned during a long-forgotten lunch break.Using my nitrogen-enhanced imagination, I envision the dredge in working condition, with stoked boilers and a hissing steam engine powering the big earth-moving bucket. Phantom workmen take their places at rusty levers, and long-stagnant gears begin to turn.Too soon, my computer signals the approach of mandatory decompression. The machinery stops, the workmen disappear, and I head for the surface and the late 20th century. A Nautical HeritageOn the ride back to the dock, I peel off my drysuit and lounge on the Northwind's forward deck. Limestone's shop manager, Doug Arnberg, joins me, and we discuss our dive plans for the coming week.There are literally thousands of wrecks scattered across the bottom of Lake Ontario, he tells me, including many not yet discovered. Of that number, there are a dozen or so historic wrecks that are most often visited by Limestone and Kingston's other dive charter operators.It's unusual to see a natural shipwreck in the excellent condition of the Munson, I observe. Not in Lake Ontario, Arnberg tells me. Instead of being dashed to pieces on reefs or hostile coastlines, many of the region's wrecks sank in mid-water.Caught unaware by sudden squalls that swept across the lake, freight schooners were pushed under before the crew could reduce sail. Steamers foundered when washed by rogue waves; bad weather and fog led to collisions in narrow shipping lanes; and winter storms tested the security of hatches and seams, finding and exploiting every weakness.A substantial number of the lake's victims went down intact, settling onto the flat, sandy bottom at depths of 100 feet or less. In the years since, the cold fresh water has held these wrecks in a remarkable state of preservation. It is not unusual, Arnberg says, to find 100-year-old timbers that still show the shipwright's chisel marks.The sheer number of shipwrecks in the region is due not only to the mercurial weather, but also the high volume of shipping that passed through these waters. Ever since explorers and fur traders first made their way up the St. Lawrence River, the settlement that would become Kingston held strategic military and commercial value. It soon became a watery crossroads for ships passing between the Great Lakes and the ocean.Kingston grew prosperous on trade and shipbuilding. Fort Henry, a 19th-century British military fortress, was constructed to protect the area from U.S. aggression, and the town served as the first capital of the united Upper and Lower Canada.Today, Kingston has evolved from an industrial port to a regional center for higher education and tourism. Historic downtown buildings house cafes and clubs, waterfront parks host festivals and concerts, and restored Fort Henry stages daily re-enactments complete with cannon fire, guns and fife-and-drum music. Our destination lies a couple of miles west of the downtown waterfront district. Cliff points the bow of the Northwind toward Portsmouth Olympic Harbor, an area recently transformed from shipyard slums to a modern water-sports center. To the east of the docks, the tall limestone walls and towers of the Provincial Penitentiary dominate the horizon."That building to the west used to be a psychiatric hospital," Cliff tells me. "I tell people this harbor is a perfect location for divers. Not quite criminal, but pretty close to crazy."It's a short walk from the harbor to the dive shop, which takes its name from the historic limestone building in which it is housed. After hanging our gear to dry, we go around the corner to decompress at an equally historic pub. Submerged MemoriesFor the next five days, the winds remain calm and the skies blue. Taking advantage, we stage visits to most all of the area's favorite wrecks.After taking the wheel of the sailing schooner George Marsh, we pose for photos alongside her bowsprit. We drop into the hold of the City of Sheboygan, then take in the massive beam engines and paddlewheels that powered the steamship Comet.A site known as the Amherst Island Graveyard yields a number of interesting finds including iron and wooden wrecks and a still unidentified ship so large it has been nicknamed the "Titanic."On the final day of my visit, a group of divers from New York requests a trip to the area's one artificial shipwreck, the Wolf Islander II. After a 30-year career carrying passengers and automobiles between Kingston and nearby Wolf Island, this coastal freighter was retired in 1976, and later cleaned and sunk for the enjoyment of divers.