Waiting for ice-out

Friends Steve and Mary Jo visited our Birch Lake retreat last week. Steve and I went ice fishing – he showed me the routine of setting tipups for walleyes. It was single-digits cold with wind gusts to 25 mph and more, blowing new snow in miniature tornadoes across the lake. Boring holes with the gasoline-power auger, we found the ice 18 inches thick.

Now February is winding down, and I’m waiting for ice-out. I’ll be waiting for a while, I realize, but I look forward to observing, for the first time ever, the thawing of a lake. I never had that opportunity until we bought our land and had year-round access to the lake. I do know that lake-dwellers keep track of ice-in and ice-out dates as major milestones of each year.

While I wasn’t there to see it, I know that the ice went out early on Birch in 2010. I waded in the lake, not at all uncomfortably, in mid-April of that year. 2011 was a different story. When our family held a ceremonial groundbreaking for the cabin on April 16, the lake was still frozen stiff, it was cold, windy and snowing, and we drank our champagne huddled inside our RV trailer.

This year all signs point to early ice-out, but of course that can change – March can still be brutal and April chilly, and the ice can linger even into May. Now that the cabin is complete, we can be there as the days finally get warm and the ice recedes. I can’t wait to watch it happen.

This wonder we call water

Early this week my wife and I took the springer spaniel, Freckles, for a walk from our Birch Lake cabin. We hiked down our private road, along a short section of snowmobile trail, and then onto the lake. Here Noelle hesitated; she had never skated or walked on a frozen lake before. Freckles had no such trepidation and tugged hard at the leash. We followed, taking an arcing path across the ice to where our pier would be in summer.

Isn’t it wondrous that we can walk on the lakes in winter, and that the water below teems with life forms, active and dormant? We owe it all to a singular property of water. Most liquids contract as they cool and keep on contracting until they solidify. Water, on the other hand, contracts until it reaches 4 degrees Celsius (39 degrees Fahrenheit), at which point it begins to expand, and continues to expand until it becomes ice. So as a lake cools down toward the freezing point (zero Celsius, 32 Fahrenheit), the densest water at 4 degrees Celsius is at the bottom. Ice forms at the surface and, because it is less dense than the water, it floats. Soon a skin of ice covers the lake, and it gets thicker with cold days and nights as winter deepens. This ice then insulates against the subzero temperatures and keeps the water below in the liquid state, in which life thrives.

Why water behaves this way is a matter of chemistry and physics – of molecular vibration, positive and negative charges, molecular shapes, hydrogen bonds and such. I don’t claim to understand it all. I do marvel at how earth’s most abundant substance – the one life depends on, the one life is made of – shows this benevolent anomaly of expanding, not shrinking, as it cools toward freezing. What if this were not so? Ice crystals forming on the surface would sink. As more and more water froze, would it begin collecting on the bottom? And would our lakes continue to freeze all winter, until they froze solid?

When walking on a frozen lake, or drilling through the ice and lowering golden shiner minnows from tip-ups to catch winter walleyes, it is wondrous to contemplate the special properties of water.

Rusty crayfish: An invasive menace

While walking on frozen Birch Lake recently I saw something I had never seen before. An ice angler ran to a tip-up displaying a flag and pulled up not a walleye but a crayfish. It was a rusty crayfish, a species native to the Ohio River valley that anglers brought to Wisconsin as bait and that has taken over a goodly number of lakes.

I thought crayfish just lay dormant all winter, but apparently not. At any rate, the rusties overran Birch Lake about 15 years ago, wiping out its rich cabbage weed beds and changing the whole structure of the fish population. Panfish and perch are all but gone, although walleyes are abundant and smallmouth bass reach genuine trophy size.

A trapping program run by the Friends of Birch Lake group has helped bring the crayfish population under control. So has increasing predation by fish and, at least according to rumor, so has a viral disease. Still, it’s upsetting to see such profound change brought on by a species that does not belong in the lake.

Invasive species – fish, plant, invertebrate – threaten many inland lakes, maybe including yours. If you want to learn about just how rusty crayfish can affect a lake, you can read my 2008 story from Wisconsin Natural Resources magazine at http://dnr.wi.gov/wnrmag/html/stories/2008/oct08/crayfish.htm.