A typical spring situation sees the south facing shoreline receiving more and more heat as the sun tracks higher in the southern sky. The background photo was taken on April 13, 1999. Note the ice melting off of those south and west facing banks and the widening strip of open water along those shores. Meanwhile the overall ice sheet is hollowing out from beneath, called “honeycombing”. Though the vast majority of the lake still appears to be covered the ice is very weak. Then a warm south wind comes up and if it is gusty enough the ice will be gone in two to three hours.

The DNR’s definition of “ice-out” is the first day that all ice is gone. Since ice out is normally a rather sudden and sometimes noisy event, these dates have been recorded here since 1909.  Emil Wiesse, who lived in Barber’s Bay (then called Wiesse Bay), recorded them through 1921.  Janet Vineyard’s family, the Handlos’, then recorded them through 1965.  Jim Lowenstine’s caretakers took over through 1997  and John Annin and Walt Bates have recorded them since then. The earliest was on March 27 (1945) and the latest was on May 17 (1996). The overall average date is April 26. The recorded dates follow:

 

 

Black Oak is known limnologically as a groundwater seepage lake. This is a water body with no inflow or outflow streams.  Water enters the lake only through precipitation or by underground flow.  We know there are significant springs in the lake by the large holes that remain in the forming ice of early winter long after the majority of the lake has frozen solid.  Water leaves the lake only through evaporation or by underground flow. 

It would be logical that the lake level would correlate with annual precipitation but long term studies on Buffalo Lake in Oneida County do not support that idea. Buffalo Lake is also a groundwater seepage lake and its level has been accurately recorded weekly since the 1940s.  DNR researchers then assumed that summer precipitation is mostly lost by either surface evaporation or transpiration from trees. Only the precipitation that falls from October through March would really make a lake level difference. When that was considered the correlation with the lake level was quite close.  And we note the same thing on Black Oak except for the summer of 2002 when there was a lot of summer rain. Recorded snowfall compared to our spring / fall water levels shows that a 70 inch snowfall winter results in no change between the previous fall and following spring. The accumulating snow during a winter is shown on page 2 of the weekly Vilas County News Review.

The Ordinary High Water Mark (OHWM) is a DNR determined level used as a basis for building setbacks and many other things. To determine this level they use things like clearly defined watermarks or where the shoreline growth changes from aquatic to terrestrial. The OHWM is also the limit of your property ownership. On Black Oak Lake this level is at approximately 45” above the reference used for the levels shown below – a height rarely reached by the actual water level. This means that there is a good bit of land in front of your property that you don’t own. But Wisconsin is one of the few states that grants riparian owners the right to exclusive use of such land. You can’t fence it but you can post NO TRESPASSING signs. Click here to go to the applicable DNR explanation pages.

An accurate water level history has been kept here only since 2001 though we do have a DNR lake bottom contour map from August, 1969. This map gives a water level that would be at 34 ¾” on the chart below, exactly like 2004. Also, some old pictures have happened to record approximate levels. Most pictures from the 1930s and 1940s show the water much lower than present levels while pictures from the 1970s show a much higher level. The Black Oak Lake history book has a photo on page 59 from the early 1930s that shows a water level that would be about zero inches on the reference stick used for the readings below. Note that we have reached that again in spring, 2010. Using the water lines on the large rocks along the north shore is not reliable as even the largest rocks are shifted by winter ice. So, in the early spring of 2001 a concrete block was buried in the bottom in about 24 inches of water near the Dirk Meyer / Walt Bates property line. It is assumed that winter ice does not disturb this block though there is a much deeper and larger  block in about seven feet of water that we use as a cross check. Depth readings have been taken over this block immediately after ice out and just before freeze up each year since it was placed and are shown below. A small though interesting factor is that according to DNR data the volume of the lake is 19,956 acre feet or 863,380,710 cubic feet. Approximately 50% of Black Oak’s water is in its epilimnion (the water above the midsummer thermocline at about 30 feet of depth). Given that water density varies 0.2% between the all lake temperature of 4 degrees C of winter and the epilimnion’s 20 degrees C of summer, the lake rises and falls just under one half inch between mid summer and the frozen time due to this warming and cooling. One more factoid: the height of the bottom of the culvert through which water can flow under Highway B towards Lake George is 26 ¾”.

WATER DEPTHS IN INCHES

YEAR

ICE OUT

FREEZE UP

2001

22"

19.5"

2002

24.5"

34.5"

2003

36"

30"

2004

34.5"

29.5"

2005

29"

32"

2006

35"

28.25"

2007

28.75"

14.5"

2008

16.5”

9.5”

2009

10.25”

2.25”

2010

0”

6.75”

2011

13.25”

6.75"

2012

2013

2014

2015

2016

Though Black Oak’s level has been accurately recorded only since 2001 there are two other area lakes where levels have been recorded since the 1940s. Buffalo and Crystal Lakes are near Woodruff and, like Black Oak, are groundwater seepage lakes. Therefore, their levels should go up and down in lockstep with Black Oak’s. CLICK HERE to see these levels and look for any regular spacing in the highs and lows – they appear to be totally random. One obvious thing is that most of the highs and lows don’t last long before things reverse, two or three years being about the longest. In reading the graph note that the data-taking on Buffalo Lake ceased in 1990 and the data-taking on Crystal Lake started in 1978. Therefore, there is a 12 year overlap and the graphs have been merged to represent a single groundwater seepage lake. The two graph colors are blue for Buffalo Lake (abbreviated BL) and pink for Crystal Lake (abbreviated CL).