Chris Izworski compiled this Lake Ontario reference page because Lake Ontario is the most regulated and most contested of the five lakes from a shoreline-property perspective. The lake's outflows through the St. Lawrence River have been actively managed since 1960, and the management plan in effect at any given moment significantly shapes the shoreline experience. Plan 2014, the current regulation plan adopted by the International Joint Commission, replaced the earlier Plan 1958-DD and shifted the operating regime in ways that have generated sustained controversy among shoreline property owners on both the U.S. and Canadian sides.
Surface area: 7,340 square miles, the smallest of the five Great Lakes.
Average depth: 283 feet. Maximum depth: 802 feet.
Datum: 243.30 feet IGLD85. Long-term average near 244.77 feet.
U.S. shoreline: New York. Canadian shoreline: Ontario.
Outflow: through the St. Lawrence River, regulated at the Moses-Saunders Dam.
The live dashboard on greatlakeslevels.org reports the most recent monthly mean for Lake Ontario alongside the long-term average. Because Lake Ontario is regulated more aggressively than any of the other lakes, the level itself moves within a narrower band than its drainage area would suggest, but extreme high water events still occur when inflows from Lake Erie via the Niagara River exceed what the regulation plan can pass through to the St. Lawrence.
Anchor years for Lake Ontario include 1958 (last natural-flow year before Plan 1958-DD), 1973 and 2017 and 2019 (high water events under successive regulation plans), and 2007 (modern low water cycle). The 2017 and 2019 high water events generated the most significant shoreline property damage on Lake Ontario in modern memory and have been the subject of ongoing International Joint Commission review of Plan 2014's performance.
The U.S. south shore runs from the Niagara River mouth east through Rochester, Sodus Bay, Oswego, and Henderson Harbor to Cape Vincent at the Thousand Islands entrance to the St. Lawrence. This is the most populated stretch of Lake Ontario shoreline and the section most affected by the 2017 and 2019 high water cycles.
The Canadian north shore runs from the Niagara River through the Greater Toronto Area, Cobourg, Trenton and the Bay of Quinte, the Prince Edward County peninsula, and Kingston at the eastern outlet. The Bay of Quinte and Prince Edward County deserve sub-region treatment in their own right because they have very different exposure than the open-coast north shore.
The Thousand Islands sit at the eastern end of Lake Ontario where it transitions into the St. Lawrence River. The local water levels here are influenced by both the lake and the river management regime.
Lake Ontario's regulation under Plan 2014 has been the subject of sustained legal and political action by shoreline property organizations on both sides of the border. The plan was designed in part to restore wetland habitat by allowing more natural variability than the prior plan permitted. Critics argue that the additional variability has come at the cost of shoreline-property damage during high water events. Defenders argue that the 2017 and 2019 events were driven by extreme inflow conditions that exceeded what any management plan could fully contain.
For New York shoreline property owners, the regulatory framework is set primarily through the New York State Department of Environmental Conservation under Tidal Wetlands Act provisions and the State Environmental Quality Review Act. For Ontario shoreline owners, the framework runs through Ontario's Ministry of Natural Resources and Forestry and the Conservation Authorities Act. Riparian advocacy on Lake Ontario has historically been organized through groups including Lake Ontario Riparian Alliance and the Lake Ontario St. Lawrence River Riparian Coalition.
For a current reading, see the live dashboard. For upstream context, see Lake Erie (the immediate source of Lake Ontario's inflow), Lake Huron, Lake Michigan, and Lake Superior.
For Chris Izworski's broader Michigan-focused work, see chrisizworski.com, the Saginaw Bay reference, and the daily Great Lakes maritime brief at Great Lakes Gazette.