Four inches of ice isn't a promise

Quick answer: Four inches of clear, new ice will hold a person on foot. That's the floor, in good conditions, measured where you're standing. Check it every hundred feet or so, trust color over the calendar, and stay off anything near moving water.

The number comes with fine print

Every ice-fishing shop and state wildlife agency repeats some version of the same chart. The Minnesota DNR's guidance for new, clear ice is four inches for walking, five to seven for a snowmobile or ATV, eight to twelve for a car or small pickup, and twelve to fifteen for a medium truck.

Read the qualifiers again. New. Clear. The chart describes ice that froze cleanly in one stretch of cold weather, and a lot of the ice you'll meet isn't that. It's been snowed on, thawed, refrozen, and stacked in layers like a bad lasagna. Four inches of that is not four inches of the good stuff.

The DNR says it plainly: no ice is 100 percent safe. Treat the chart as a minimum that earns you permission to keep checking.

Read the color first

You can learn a lot before you ever drill a hole.

• Clear blue or black ice is the strongest. It froze slowly and solid.
• White or opaque ice is usually snow ice, formed when slush froze. It's commonly rated at about half the strength of clear ice, so four inches of white is closer to two inches of the real thing.
• Gray ice has water in it. Stay off.
• Honeycombed, dark, or "candled" ice in late winter is rotting. It can be a foot thick and still drop you through, because the crystals have come apart.

Snow on top matters too. It insulates the ice and slows freezing underneath, so a lake with a foot of early snow can be dangerously thin under a blanket that looks like solid ground.

One hole is a rumor

Ice doesn't freeze to a uniform thickness. It can be eight inches at the boat ramp and three inches forty yards out.

So carry something to measure with. An auger is best. A spud bar, which is a long steel chisel, works fine and also lets you test the ice as you walk. A cheap tape measure with a hook on the end completes the kit. Hook it under the bottom edge of the ice and read it there. Don't count the slush layer sitting on top.

Drill a hole every hundred feet or so as you head out, and again any time the ice color changes. Walking out with your spud bar, give each step a firm strike. If it punches through in one or two hits, turn around. That's the ice telling you what it thinks of the plan.

Start from shore. Don't test the edge by jumping on it.

Where the ice is thin no matter what

Some spots stay weak all winter, no matter how cold it's been.

• Inlets and outlets, where moving water keeps eating at the underside
• Narrows between points and anywhere you can feel current
• Around docks, pilings, and bubbler systems that keep water open on purpose
• Near rocks, stumps, logs, and reed beds, which soak up sun and melt the ice around them
• Pressure ridges and long cracks, which mean the sheet is shifting
• Springs, which you can't see and which can feed a thin patch in the middle of a thick lake
• Under bridges and near any shoreline where a creek comes in

Rivers are their own problem. Current changes the ice from week to week, and what held on Saturday may not on Sunday. Learn a river's ice from somebody who has fished it for years, not from a chart.

Early and late season are the two riskiest windows. In early season the ice hasn't had time to build. In late season it's been weakening from the top down and the bottom up, and a warm afternoon can undo a week of work. Our piece on the weather that kills hikers covers reading a forecast for the swings that matter here.

What goes in the bag

A short list, and every item is cheap compared to what it protects.

• Ice picks worn on a cord around your neck or on the outside of your jacket, not buried in a pocket. They're two handles with spikes, and you'll want them in your hands in seconds.
• A life jacket or float coat. It's the one thing that keeps your head up after the cold shock hits.
• A throw rope, fifty feet or so, in a bag you can toss one-handed.
• A spud bar for testing the ice ahead of you.
• A whistle and a phone in a zip bag.
• A dry bag with a full change of clothes left in the truck, so you have something to put on when you come off the lake.

Go with a partner, and spread out so one weak patch doesn't take both of you. Tell somebody where you're going and when you'll be back. That's the same habit as the ten essentials, and it works just as well on a frozen lake.

If you go through

The first thing that happens is a gasp, and a lot of the danger comes from that. Cold water forces involuntary fast breathing for the first minute or so. Cold-water researchers popularized the 1-10-1 rule: about one minute to get your breathing under control, about ten minutes of useful movement in your arms and legs, and about an hour before hypothermia knocks you out.

Use the ten minutes.

1. Don't thrash. Get your breathing back first.
2. Turn toward where you came from. That ice held you a moment ago.
3. Get your arms up on the edge and dig in with the picks.
4. Kick your legs flat behind you, like you're swimming, until your body slides onto the ice.
5. Roll away from the hole. Don't stand up. Spread your weight and keep rolling until you're well clear.

Then get warm immediately. Dry clothes, a heated truck, and a hot drink if you have one. Wet clothes steal heat fast, and so does the ground, as we explain in the ground steals your heat before the air ever does. Get checked out afterward. Hypothermia can keep working after you feel fine.

If somebody else does

Reach, throw, don't go. Your instinct is to run to them, and that's how a rescue turns into two victims.

Lie flat, if you have to approach at all, and push a pole, ladder, branch, or rope toward them. Throw the rope from a distance. Call 911 first or have someone else do it while you work. Once they're out, treat them for hypothermia the same way: dry, warm, and watched.

Be the one who says no

Most ice accidents aren't about people who didn't know the chart. They're about a group of guys where somebody wants to go out a little farther, and nobody wants to be the guy who says no.

Be that guy. It costs you a few minutes of ribbing. "Somebody's out there on a four-wheeler" isn't a measurement. Neither is "it was fine last week." If you've got kids with you, they stay close to shore and on your rules, and you check the ice before they step on it, not after.

Leave the lake cleaner

Everything you leave on the ice goes into the water when it melts. Pack out your line, your bait containers, your cans, and your tip-up pieces. Pull your shelter before your state's removal deadline, and know what that date is. Pick up whatever the last guy left behind, even if it isn't yours. A lake you've fished should look like you were never there, except for the fish in the cooler.

The lake will be there in January. Make sure you are too.