NEW YORK - A team of shipwreck explorers has discovered a mid-19th century sunken steamship, believed to be the oldest of its kind ever found in Lake Ontario, one of its members said on Tuesday.Jim Kennard and Roger Pawlowski found the wreck off the lake's southern shore in upstate New York in August after months of fruitless exploring using a sonar system."We were thrilled," said Kennard, a diver and lake shipwreck expert. "It had been a really bad season for us because of wind and waves and then long hours on the lake and finding nothing."Kennard and his partner first spotted the ship when they passed over it in their own vessel while scanning the lake, which reaches depths of 800 feet (74 meters).They measured the wreck using sonar and identified it using a database Kennard created of 600 ships that have sunk or been wrecked on Lake Ontario over the past 350 years.The vessel, measuring 137 feet (42 meters) with a beam of 26 feet (8 meters), was known as the Bay State, according to the database, which used local newspaper articles published at the time.It was near Oswego, New York in November 1862 during the US Civil War when a violent storm hit, sinking the ship and killing as many as 18 people aboard.General merchandise aboard and bits of the wooden vessel itself washed ashore in Oswego in the days following, according to the news articles. Locals helped themselves to the goods.Some 6,000 to 8,000 ships have been wrecked in the Great Lakes, often by being driven ashore, burned in harbors or smashed to pieces. Today, about 200 ships remain in Lake Ontario, which borders Canada to the north.Over the past four decades, Kennard has found more than 200 shipwrecks in the Great Lakes, Lake Champlain, New York's Finger Lakes and in the Mississippi and Ohio Rivers.Only one older propeller-driven steamship is known to have disappeared in Lake Ontario. It has never been found.So little is known about the steamships that maritime researchers are eager to study the find, Kennard said."We're really bringing maritime history to the surface," he said.The wreck itself, which is considered historic and belongs to the state of New York, will remain in place. Researchers will study images captured by Kennard and Pawlowski.