Rapids of the Upper Ottawa
For over two centuries the Ottawa River was part of the main canoe route to the West. Some of the river's most spectacular and dangerous rapids were located immediately downriver from here: the Rapide de la Veillee, the Trou and the Rapide des Deux Rivieres. Further on lay the legendary Rapide de la Roche Capitaine. In 1800 the explorer Daniel Harmon counted fourteen crosses commemorating voyageurs who had drowned in its swirling waters. By 1950, with the construction of the Des Joachims generating station, these rapids and their portages had been submerged in the dam's headpond, Holden Lake.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.