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Message: <blockquote data-quote="Allen" data-source="post: 314518" data-attributes="member: 389">While ice does indeed float, there's also what's called ice bridging.  Basically, it happens when a reservoir is lowered after ice cover is developed, the ice in the middle of the lake is floating on top of the water, but as you get close to shore, thick ice will sometimes "bridge" from the shoreline to where it is floating on top of the water some distance from shore.  Now, 5-6 ft would be an awful lot of bridging, certainly more than I have ever witnessed and would only ever be seen next to a very steep drop off on a reservoir that has been lowered by at LEAST 5-6 ft since ice cover developed.  Nonetheless, the ice surface would likely be so steep as to give you a clue that something is amiss.  In general, the water in the hole should be down about 10% of the overall ice thickness for it to be properly floating on the water.  So if the ice is 10 inches thick and without a heavy snow cover on the lake, the water level should be about an inch below the surface of a freshly drilled fishing hole. If the water level is more than 10% of the ice thickness below the surface of the ice, it is being bridged to some extent.This was the primary reason Jamestown and Pipestem reservoirs had their access restricted during the 2019-2020 winter. We often see the unlevel ice at access points on our bigger reservoirs (Sak and Oahe), but don't really think much about it as we drive down the boat ramps to get on the lake.  Needless to say, the transition from unlevel ice to that floating on the water is the danger point as ice without water support isn't very strong for its thickness as it requires its buoyancy to help hold vehicles up and keep them from falling through.  Thankfully, it is very rare that we see reservoirs needing to be lowered 5-6 ft over the course of a winter.  Most tend to go into winter with 3 ft or less of water that needs to be discharged over the course of winter.</blockquote>

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