In 1953 European frog-bit had been found at the Rideau Canal exit and along the shore of the Ottawa River. In 1957 Hydrocharis had been found in the main channel of the Rideau River. By 1960 European frog-bit had been discovered in various locations in the Ottawa River around Montreal and much farther downstream at Lake St. Peter. Intervening stations along the shore of Lake Ontario in the vicinity of Toronto had been recorded by 1986. Although its initial spread was confined to the Rideau and Ottawa River systems, it soon found its way into many isolated and unconnected wetlands and waterways.
Solid circles represent individual or local occurrences.
It has small white unisexual flowers that open just above the water surface. In spring these turions rise again to the surface and begin growing. Ecology Few studies have been conducted on the ecological impact of European frog-bit. Catling et al . Because of the dense floating mat of vegetation produced by European frog-bit, available light, dissolved gases, and nutrients were restricted to submerged aquatics attempting to grow beneath this mat.