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Historical Lake Levels- Lake Ontario

This page is part of the project: Great Lakes Climate Change and Lake-Levels

Lake Ontario


Lake Water Levels: Historical Monthly Data

Data Source: Glerl (NOAA)

Points of Interest: The current Welland canal was completed in 1932 (it is the fourth canal). The first, second, and third canals were built in 1829, 1845, and 1887, respectively. These canals are used for ships to bypass the Niagara River (which contains Niagara falls) and travel between Lakes Erie and Ontario.

Info on monthly data: The data comes from the Great Lakes Environmental Research Lab (GLERL) and spans from January 1860 until September 2016. The data from 1860-1917 comes from a master gauge that was present on each lake. These gauges might not represent the true lake-wide average level if they were far from the lake's outlet due to isostatic rebound. From 1918-2016, there were more gauges present on the lakes (at present 53 monitoring stations in the US and 33 stations in Canada) which gives a more accurate representation of the lake's water levels. For more information on the gauges visit:

The data set used to make these figures was a combination of the master gauge data from each lake (the 1860-1917 data) and the 1918-2016 water level data that comes from GLERL. These data sets were processed using Python code created by GLISA which created a certain output, in this case a csv file (access below).

Great Lakes water levels are measured from an elevation reference point referred to as the International Great Lakes Datum of 1985 (IGLD 85). This datum is referenced to sea level as measured at Rimouski, Quebec, near the mouth of the St. Lawrence River. Every 25-30 years, the IGLD is changed to account for crustal movement–the ‘bouncing back’ of the earth’s crust from the weight of the glaciers. This datum is the average water level line in the graph.

Data Access: /media/u3841/files/Monthly_lake_levels_ontario.csv


Lake Water Levels: Decadal Averages

Decade Water Levels (m) Standard Deviation
1861-1870 75.03 0.30
1871-1880 74.77 0.28
1881-1890 74.97 0.28
1891-1900 74.54 0.27
1901-1910 74.79 0.31
1911-1920 74.78 0.27
1921-1930 74.69 0.31
1931-1940 74.34 0.27
1941-1950 74.90 0.34
1951-1960 74.90 0.38
1961-1970 74.65 0.28
1971-1980 74.92 0.31
1981-1990 74.84 0.24
1991-2000 74.83 0.29
2001-2010 74.79 0.24
2011-2015 74.77 0.26
Data Source: Glerl (NOAA)


A box and whisker graph showing average lake levels on decadal (10 year) time scales. For example the box on 1861 is the average from 1861 to 1870, the box on 1871 is the average from 1871 to 1880, and so on. The red line in the box is the median for that decadal average, the top and bottom of the box are the 75th and 25th percentiles, the dashed lines are the extreme data points not considered outliers, and the red '+' signs are the outliers.


Lake Water Levels: 30 Year Averages

30 Year Period Water Levels (m) Standard Deviation
1861-1890 74.92 0.30
1871-1900 74.76 0.33
1881-1910 74.77 0.33
1891-1920 74.71 0.30
1901-1930 74.76 0.29
1911-1940 74.60 0.35
1921-1950 74.64 0.39
1931-1960 74.71 0.42
1941-1970 74.81 0.35
1951-1980 74.82 0.35
1961-1990 74.80 0.30
1971-2000 74.86 0.28
1981-2010 74.82 0.26
Data Source: Glerl (NOAA)

A box and whisker graph showing average lake levels on 30 year time scales. For example the box on 1861 is the average from 1861 to 1890, the box on 1871 is the average from 1871 to 1900, and so on. The red line in the box is the median for that 30 year average, the top and bottom of the box are the 75th and 25th percentiles, the dashed lines are the extreme data points not considered outliers, and the red '+' signs are the outliers.


Annual Water Level Cycle
Data Source: Glerl (NOAA)
Note: The average was done using monthly data from 1860 to 2016.

The high water level period for Lake Ontario is early to mid-summer (May-July range) and the low water level period is late fall to winter (Nov-Feb range) which can be seen in the graph above. There can be year-to-year variations but these time ranges are the average time period that the lake experiences its annual high or low water mark.


Data Source: Glerl (NOAA)


When comparing the annual cycle of the lake level from the present decade going back to the 1860s, there hasn't been a significant change in the time during the year that the low and high water marks occur. The lows in each 30 year period all still occurred in December-January range, with the exception of the most recent period which occured in November, and the highs occurred in June. This could mean that if the timing of the high/low in the annual cycle is changing, it hasn't changed by a large time range to be seen. That is, the data is monthly so if the timing of the high/low has changed by a week or two, it would be hard to see as it could still occur in the same month of the year just a different week in that month.
Sustained Periods of High/Low Water Levels