Known as "First Rapids" prior to construction of the Rideau Canal, the name signified the first set of rapids encountered as the Rideau River flowed from Rideau Lake. During canal construction an officer of the Royal Engineers named this site Poonamalie as he was reminded of India by the majestic arbour of tall cedars veiled in the mists of First Rapids. The two names appear to have been used inter-changeably until the latter half of the 19th century when the name Poonamalie prevailed.
In the construction of the canal, to overcome the obstacles posed by First Rapids, a dam was built to raise the water in the river and a cut, approximately one and a half miles long. dug to provide access to a lock with a six foot four inch lift (1.9m). Located beside the lock is the defensible lockmaster's house, erected in the 1840s and later modified during the late 19th century with the addition of a second storey. Immediately south of the boat launch is the Keegan House, an impressive early 19th century farmhouse.