Good weather and surprisingly clear water conditions in Lake Ontario have aided a group of marine archaeologists in their underwater study of a 19th century shipwreck that lies in the shadows of Toronto's CN Tower. The Sligo was built in 1860 and sailed the Atlantic Ocean and the Great Lakes until her demise in 1918.

The 48 metre long ship sits upright on the bottom of Lake Ontario . Much of her deck and railing forms a debris field in the mud around the downed ship. A donkey winch used to load limestone gravel can be seen inside the wreck. The ship's wheel has somehow escaped damage and still stands upright attached to the hull of the Sligo, 22 metres below the surface of the cold waters of the Toronto harbour.

The Sligo is not a newly found wreck. The remains of the wooden freighter were discovered in 1980, two kilometres offshore from the mouth of the Humber River just west of downtown Toronto . However, because of high pollution levels, low water visibility and busy boat traffic in and out of the Toronto Harbour, no serious archaeological expeditions have been made to the Sligo Š until now.

Kimberly Monk, the former president of the Toronto chapter of Save Ontario Shipwrecks (SOS) and now a graduate student at East Carolina University in Greenville , North Carolina is leading a group of scientists and volunteers in the month long underwater study of the Sligo . Each morning since early June, a donated tender boat from the posh Boulevard Yacht Club heads out into the lake where it moors near a bobbing upside down Javex bottle that marks the gravesite of the Sligo. It is on the bottom of the lake where this diving researcher spends her time measuring, photographing and taking core samples of the 52 metre long wreck.

"I have been just blown away by the clarity of the water. Based on preliminary dives I made three years ago, I expected that we would have had trouble not only seeing the wreck but actually photographing her," said Toronto native Kimberly Monk. "We were expecting to need strong lights for our cameras, but, conditions are so good you can almost see her from the surface of the Lake !"

Ms. Monk is interested in the Sligo because of her unique place in Maritime history. Originally built as the three-masted bark, the Prince of Wales, she made several trips from Toronto to the United Kingdom and South Africa . After years of service she was rebuilt as a schooner, renamed Sligo and then exclusively employed for the inter-Great Lakes markets. Much later Sligo was cut down for use as a tow barge, when the costs of sailing and manning ships outweighed the costs of operating steam tugs. The ship's career ended in 1918 when she sunk within hailing distance of shore.

The prolific 19th century boat builder, Louis Shickluna, constructed the ship uplake in Saint Catherines , Ontario . Shickluna shunned standard British marine designs and constructed the ship based on the dimensions of what was then the recently rebuilt Welland Canal .

"The Sligo was a Welland sailing canal ship. This style of boat was the first made-in-Canada, Great Lakes vessel type. She was the epitome of a workhorse vessel," explained Ms. Monk. "You can see why Louis Shickluna [1808-1880] designed her the way he did. It had everything to do with being able to squeeze through the Welland Canal with the maximum cargo space available-- that meant a maximum length of 45 metres, a width of 8 metres and draft of only about 3 metres. To hold the water when she sailed (across the Atlantic ) she had a 3 metre long centerboard."

"People in Toronto don't realize that there is a major marine artifact lying literally at the foot of the city," explains marine archaeology student Kimberly Monk. "This summer we are going to study the ship's design and examine closely how she was modified from a bark, to a fore and after freighter and then finally a bark."

Because the Sligo was so old when she sank, no effort was made to raise her. She was filled to the gunnels with limestone pellets that were meant to be used in the construction of what is now the QEW highway. The road builders didn't feel it was worth the effort to recover her cargo of stone. Although the ship's sinking was well documented by the Globe and Mail, the wreck of the Sligo was soon forgotten.

Veteran diver Don McIntrye rediscovered the Sligo in 1980. Soon dive clubs and wreck associations began to dive on her, but because of the numbing cold temperatures of the water, the poor visibility and the red tape it takes to dive on her [the sunken remains lie within the jurisdiction of the Toronto Harbour so divers must register with the Harbour Commission prior to entering the water], the wreck is not well known by sport scuba divers.

"Recreational divers do visit the Sligo , but in small numbers. The visibility has gotten better in the past few years, but, it certainly isn't what I would describe as a popular wreck site," said Ms. Monk.

First hand experience by this writer found that even on a scorching hot day in July, the water around the Sligo is near freezing -- 6 degrees Celsius. It is suitable only for people with cold water diving experience and the proper gear.

"I think some of the divers have removed artifacts from the Sligo . There were dishes, plates and cutlery on her deck when I dove her in 1999, but there are still many things that should be protected that still on her," said Ms, Monk. "The ship is beginning to break apart and the deck is collapsing, It is possible that some of the missing artifacts are actually covered by the fallen deck."

The increased visibility that the marine archaeologist speaks about is a positive side effect to what is considered an environmental disaster -- the Zebra Mussel. The European mollusk has invaded the Great Lakes , attaching themselves to rocks, docks and shipwrecks. Each tiny zebra mussel filters up to a litre of water a day, taking in murky water and spitting out clean in its place. In the eastern end of Lake Ontario , water clarity has increased by 77 percent.

The clarity is a double-edged sword for the researchers. They had budgeted a week of diving to take pictures of every metre of the ship. But when photographers Doug Arnberg and Tom Wilson swam over the deck of the Sligo they found the conditions perfect. Mr. Amberg was able to make a complete digital image of the downed ship and the surrounding debris site in just two half-hour dives.

The downside? The mussels colonize in such huge masses that their weight alone is beginning to collapse the fragile shipwreck.

"It is so bad throughout the Great Lakes that we can't even see the form of some wrecks," said Brendon Baillod, a diver and director of the Milwaukee-based Great Lakes Shipwreck Research Foundation. "They're ruining some of the most historic and best-preserved wrecks in the world."

"Once we finish our diving we will head in doors and create a photo montage that will show the complete wreck site," continued Ms. Monk. "I think people will be shocked to see how the Zebra Mussels have distorted the shape of the Sligo ."

By August she hopes to have the photo montage of the wreck site completed and a better understanding of Toronto 's little known shipwreck. The montage was supposed to go on display in Toronto 's Maritime Museum , The Pier this fall. However, on July 2nd, while Monk and four volunteer divers were measuring the Sligo 's keel, the city quietly closed the Pier, a victim of civic budget cuts.

"It is a great wreck and it is something that divers should make a point of seeing," continued Ms. Monk. "I was hoping that the non-diver could see her as well. There are a number of marine museums in Ontario , that we could work with but, there is nothing in the Sligo's homeport of Toronto .