Principal rivers flowing into Lake Ontario, New York side:

- Genesee River (4,430 cu ft/sec average discharge)
- Oswego River (6,742 cu ft/sec avg)
- Black River (no outflow given; from personal experience I can say it’s very close to that of the Oswego River, so arbitrarily set it at 6,500 cu ft/sec)
- The other minor streams in the Lake Ontario watershed (Eighteen Mile Creek, Salmon River, Sandy Creek, Chaumont River, etc.) are nowhere as extensive as the big three, so arbitrarily assume a 1,000 cu ft/sec flow for them in total.

This gives us 18,672 cu ft/sec average flow for New York rivers other than the Niagara.

If the wiggly blue lines on physical maps of Ontario do in fact represent rivers, Natural Resources Canada is doing a remarkably good job of keeping their identities secret. Two river systems I know are there are the Trent and the Caztaraqui – the latter’s mouth is at Kingston, where the St. Lawrence takes up Lake Ontario’s outflow, but my assumption is that if Lake Ontario were an empty depression, it would flow ‘upstream’ down the slope of the former lake bottom to aid in refilling the lake before any water went down the St. Lawrence.

There are no figures giving rate of flow for Ontario Rivers. In view of the fact that the land is less rugged and the Lake Ontario watershed somewhat less extensive than New York’s, make an arbitrary guess of 2/3 of News York’s flow, or 12,000 cu ft/sec.

The total discharge into Lake Ontario from state and province is therefore on the order of 30,000 cu ft/sec. Taking 1833 cu meters/sec and converting to cubic feet, we get 64,770. So the Niagara River contributes slightly over two-thirds of the total inflow into Lake Ontario, but the other streams discharging into it appear to contribute about another scant third. Granted, this is making some arbitrary assumptions, but they are ones I believe are justified from observation of flows and terrain.