Vol. 184 July 2011 

Great Lakes Spring Summary

Each of the Great Lakes experiences a seasonal 

rise in water levels each year. This exact timing 

and magnitude of this rise varies from year to 

year for each lake based on the location of that 

particular lake as well as the weather for that 

particular season. This update article will focus 

on the increases in water levels for the Great 

Lakes this spring compared to other years, and 

also discuss in more detail the factors that 

influence this rise. 

Lake Superior

The seasonal rise for Lake Superior typically 

begins in March. This is much later than both 

Lake Erie and Lake Huron which typically see 

their rise begin December or January. One reason 

for this is the difference in geographical locations 

between the lakes. The Lake Superior basin 

consists of the most northern watersheds located 

in the Great Lakes drainage area. Much of the 

precipitation that falls during the winter falls as 

snow and stays frozen throughout the winter. The 

runoff from this snowpack that works its way into 

Lake Superior is a major component of the supply 

of water to that lake during the spring. Many 

portions of the watershed draining into Lake 

Superior still contain snow into the month of May 

and it takes more time for that runoff to work its 

way into the lake, which contributes to the 

seasonal rise. 

As precipitation begins to fall as rain instead of 

snow, that water also works its way through Lake 

Superior’s various sub-watersheds and into the 

lake. Total precipitation is typically higher 

during the spring months for Lake Superior which 

also contributes to the rise throughout the spring. 

Figure 1: Lake Superior Monthly Precipitation 

Figure 2: Lake Superior Seasonal Rise

Great Lakes

Update 
- 2 - Great Lakes Update July 2011 

Figure 2 shows the rise in water level for Lake 

Superior from its lowest water level in the spring, 

and then continuing to its level as of the end of 

June. The rise is shown for this year, last year, 

and also for the historical average. Note that 

although the rise typically begins in March, this 

can vary from year to year. The last important 

thing to note on this graph is that each line is 

showing the rise in water level from the lowest 

point, not the actual water level value. The actual 

lowest water level that the lake reached each of 

these years was different, however, this analysis 

is focused on what the total rise in the water level 

was so the lowest level reached before the spring 

rise is considered the zero point for each year. 

Similar figures are shown later in this summary 

for the other Great Lakes. 

As shown in Figure 2, the total increase in water 

level for Lake Superior by the end of June for this 

season was 35cm. This was 9cm more than 

average and 25cm more than last year. After 

examining Figure 1 it is clear to see the difference 

in precipitation totals between this year and last 

year and then see the influence this had on the 

water levels. 

Lakes Michigan-Huron

The seasonal rise for Lakes Michigan-Huron (MH) typically begins about one month earlier than 

for Lake Superior, with the rise beginning in 

February. Like Superior, the runoff from the 

melting snowpack is also an important 

component to the spring rise, however due to the 

geography of the lakes the snow melts a bit 

earlier in the year. 

Figure 3: Lakes M-H Monthly Precipitation 

Figure 4: Lakes M-H Seasonal Rise

It’s important to note that the seasonal rise for 

Lakes M-H in 2010 didn’t begin until March due 

to the dry conditions for that season while the 

water level started rising in February this season. 

The total rise of 50cm for this season was 25cm 

more than average and 32cm more than last 

season. 

Lake Erie

The seasonal rise of Lake Erie is affected by the 

same factors as the upper lakes. However, due to 

the location and size of the watershed, the water 

level normally begins rising in January. The 

drainage basin for Lake Erie is smaller than the 

previously mentioned lakes; therefore the 

response in water level due to runoff from the 

watershed is typically faster. 
- 3 - Great Lakes Update July 2011 

Figure 5: Lake Erie Monthly Precipitation 

Figure 6: Lake Erie Seasonal Rise

The rise in the water level for Lake Erie this 

season has been dramatic. The monthly mean 

water level in February was 23cm below the long 

term average (LTA) water level for that month, 

and now after this swift rise the monthly mean 

water level for June was 25cm above the LTA. 

Again, this was driven by the dramatically high 

precipitation totals experienced throughout the 

Erie drainage basin over the course of the spring. 

Lake Ontario

The outflows from Lake Ontario are regulated 

through control structures along the St. Lawrence 

River. The regulation strategy has an impact on 

the level of Lake Ontario and its seasonal rise, 

however the lake level tends to follow a similar 

pattern from year to year. 

Figure 7: Lake Ontario Monthly Precipitation 

Figure 8: Lake Ontario Seasonal Rise

Like the other lakes discussed, Lake Ontario’s 

water level experienced a very large rise this past 

spring. Again, Figure 7 shows the higher than 

average monthly precipitation totals for this year. 

The peak rise of Lake Ontario’s water level was 

roughly 100cm, which is almost twice as much as 

a typical seasonal rise. Due to heavy rain in June 

of last year, the 2010 water level had a late 

increase, bringing the rise for that season to near 

average. Outflows from Lake Ontario were close 

to average for the past three months, and the 

water level rise was still significant. This again 

highlights the major impact precipitation and 

runoff into the lake have on water levels. 
- 4 - Great Lakes Update July 2011 

Summary

As shown through the rises in water levels for 

most of the Great Lakes this spring, increased 

precipitation and the associated runoff into the 

lakes can have a major impact on water levels. 

Lake Erie is a clear example of how several 

months of above average precipitation can bring a 

water level that was below LTA to above its 

LTA. To continue monitoring the lake wide 

average water levels for the Great Lakes please 

see the U.S. Army Corps of Engineers website at: 

http://www.lre.usace.army.mil/greatlakes/hh/grea

tlakeswaterlevels/