SS Manasoo (originally named Macassa) was a steel-hulled Canadian passenger and package freighter in service between 1888 and 1928.

On September 14, she left the Manitoulin Island port of Manitowaning, Ontario, under the command of Captain John McKay.

Five crewmen and one passenger climbed onto a life raft; one of the crew later died of exposure, while the rest were rescued by the steamer Manitoba.

The location of Manasoo's wreck was unknown for nearly 90 years, until it was found on June 30, 2018, by Jerry Eliason and Ken Merryman of Minnesota, and Cris Kohl of Windsor, Ontario.

Beginning in the mid-1840s, Canadian companies began importing iron vessels, prefabricated by shipyards in the United Kingdom.

[4][5] Steam for the engine was provided by a single coal-fired, 12.6-by-10.9-foot (3.8 m × 3.3 m) Scotch marine boiler, which had a working pressure of 150 pounds per square inch (1,000 kPa).

[10] The engine was built by William Kemp of Glasgow, Scotland, while the boiler was manufactured by Burnett & Company of Govan.

[4][5][6][12] While in Hamilton on August 11, 1892, a deckhand on board Macassa leaned against a gangway whilst trying to fill a bucket of water, fell overboard and drowned.

[13] She made a 39-mile (62.8 km) trip between Burlington and Port Dalhousie, Ontario, on April 6, 1894, in an hour and fifty minutes.

[5] The lengthening significantly decreased Macassa's length-to-beam ratio, causing her to roll badly even in moderate weather.

[4][5] Late in the summer of 1912, Macassa ran a special service from Coburg, Port Hope, Bowmanville, and Oshawa, Ontario, to Toronto, where she ferried passengers to and from the Canadian National Exhibition.

[4][5] While with Canada Steamship Lines, Macassa frequently travelled between Grimsby, Ontario, Hamilton and Toronto.

[28] A life raft broke loose when Manasoo sank; only six of the crew, including Captain McKay were able to climb aboard.

[28] Although the specific reason for Manasoo's sinking remains unknown, the shifting of the cattle is believed to be partly responsible.

[19][27][30] It was rumoured that Manasoo had previously been discovered by a diver resting in 150 feet (45.7 m) of water, 0.5 miles (0.8 km) from shore.

[27] Her wreck was discovered on June 30, 2018, after a four-day search using side-scan sonar, by shipwreck hunters Jerry Eliason and Ken Merryman of Minnesota, and maritime historian Cris Kohl of Windsor, Ontario.

[27] He had found a newspaper account published in 1928, which stated that Manasoo's wreck had been located a few weeks after she sank.

[27][35] The wreck is intact, although encrusted with zebra mussels, with its stern buried in the lake bottom and the bow pointing upwards at a 10° to 15° angle.