Is Lake Ontario Connected to the Ocean?

Not directly. Lake Ontario is the last (downstream) of the five Great Lakes—entirely within North America, straddling the U.S. (New York) / Canada (Ontario) border.

The Connection Path

Water flows: Lake Superior → St. Marys River → Lake Huron → St. Clair River → Lake St. Clair → Detroit River → Lake Erie → Niagara River (Falls) → Lake Ontario → St. Lawrence River → Gulf of St. Lawrence → Atlantic Ocean.

Key Points

• St. Lawrence River is the outlet—but it's a river, not an ocean.
• No saltwater intrusion reaches Lake Ontario (Niagara Falls is a permanent barrier).
• Lake Ontario is freshwater (salinity < 0.1 ppt).
• Seaway access: The St. Lawrence Seaway (locks, canals) allows ocean-going vessels to reach Lake Ontario (and all Great Lakes) — but they transit freshwater the entire way.

So: Lake Ontario → River → Gulf → Ocean. It's hydrologically connected but not directly adjacent to any ocean.