How deep is Lake Ontario?

Lake Ontario is more than 690 feet deep. The deepest contour in the NOAA NCEI Great Lakes bathymetry survey is the 690 foot line, and the lake continues deeper inside it, with 11 depth bands mapped in total.

Where is the deepest part of Lake Ontario?

The deepest surveyed water on Lake Ontario sits toward the southeastern corner of the lake, inside the 690 ft contour. The interactive depth map above shows the full basin outline and the breaks leading into it.

How accurate is this Lake Ontario depth map?

The contours come from the NOAA NCEI Great Lakes bathymetry survey. Depths change over time with water levels and sediment, so treat this map as a planning guide for fishing, and never use it for navigation. The NOAA compilation maps open-lake survey lines spaced 500 to 2,500 meters apart, so it shows whole-lake basin structure rather than individual reefs or drop-offs.

Great Lakes lake depth maps

Lake Ontario depth map

Lake Ontario in the Great Lakes basin reaches a depth of more than 690 feet at its deepest surveyed contour. The official Great Lakes survey maps 11 depth bands across 529 contour lines. This free map of Lake Ontario shows every surveyed contour as an interactive depth chart you can use to plan a session before you travel.

Lake Ontario depth chart: 11 depth bands to 690+ ft

Data: NOAA National Centers for Environmental Information, Great Lakes bathymetry (public domain), retrieved August 2026 · depths change over time · not for navigation

Lake Ontario depth chart data
Depth contour	Share of mapped area inside it
3 ft	about 36%
60 ft	about 22%
120 ft	about 16%
175 ft	about 16%
235 ft	about 16%
470 ft	about 1%
690 ft	about 1%

Share of the surveyed surface area enclosed by each depth contour, computed from the NOAA NCEI Great Lakes bathymetry data.

How to fish Lake Ontario: deep, two-story water

At 690 feet, this is a two-story fishery: warm-water species work the shallows and weed edges while the deep basin can hold cold-water fish below the summer thermocline. In summer, target the transition where the bottom breaks from the shallow shelf toward the basin; fish suspend along that edge at dawn and dusk. The 11 mapped depth bands make it straightforward to find those breaks before you launch.

Ice fishing on Lake Ontario

On deep water like Lake Ontario, the winter bite concentrates along the first major drop-off rather than the deepest basin. Use the contours above to find where the shallow shelf breaks toward deep water and set up on that edge; panfish and walleye slide up and down it through the day. Late ice often pushes fish shallower again. Always verify ice thickness locally before walking out, and remember deep lakes freeze later and less evenly than shallow ones.

Lake Ontario depth map FAQs

How deep is Lake Ontario?: Lake Ontario is more than 690 feet deep. The deepest contour in the NOAA NCEI Great Lakes bathymetry survey is the 690 foot line, and the lake continues deeper inside it, with 11 depth bands mapped in total.
Where is the deepest part of Lake Ontario?: The deepest surveyed water on Lake Ontario sits toward the southeastern corner of the lake, inside the 690 ft contour. The interactive depth map above shows the full basin outline and the breaks leading into it.
How accurate is this Lake Ontario depth map?: The contours come from the NOAA NCEI Great Lakes bathymetry survey. Depths change over time with water levels and sediment, so treat this map as a planning guide for fishing, and never use it for navigation. The NOAA compilation maps open-lake survey lines spaced 500 to 2,500 meters apart, so it shows whole-lake basin structure rather than individual reefs or drop-offs.

Depth maps for lakes near Lake Ontario

Lake Erie depth map · 205+ ft max · 196 mi away
Lake Huron depth map · 755+ ft max · 219 mi away
Lake St. Clair depth map · 25+ ft max · 252 mi away
Lake Michigan depth map · 900+ ft max · 413 mi away