First Ice: How to Read It and Check It Safely

No ice is ever 100% safe. Check it yourself.

What is first ice, and how do you check it?

First ice is the first sheet of ice that forms on a lake after freeze-up begins. It is thin, it is uneven, and it is hard to judge. The Minnesota DNR says to wait for at least 4 inches of new, clear ice before you consider walking out. That is the minimum for foot travel. It is not a promise.

To check first ice, go with a partner and tell someone your plan. Start near shore. Use a spud bar, auger or drill to make a hole. Put a tape measure down the hole until the hook catches the bottom of the ice. Read the inches. Then stop and check again as you go, because ice thickness can change a lot over a short distance. Wear a foam life jacket and carry ice picks.

Look at the color too. Clear ice, which can look blue or black, is the strongest. White ice is only about half as strong. If you are on white ice, double the thickness you need. If there is slush on the ice, stay off.

No ice is ever 100% safe. Check it yourself.

Why first ice is risky

Early ice looks solid long before it is. Wisconsin DNR says early ice covers "may look solid, but they're far from it" and are "too thin and too weak to support human or machine weight." The ice also hides currents, debris and springs that make weak spots.

Minnesota DNR says ice seldom freezes uniformly. It "may be a foot thick in one location and only an inch or two just a few feet away." Even if you find 4 to 6 inches in one spot, the same lake will likely have spots under 4 inches.

New ice is not always weak ice, though. Minnesota DNR notes that 4 inches of clear, newly formed ice may support one person on foot, while a foot or more of old, partially thawed ice may not. Age and type of ice matter, not just inches.

How to read the ice: types and strength

Clear ice (black or blue ice). Minnesota DNR calls clear ice the strongest and safest ice. It typically forms at the start of the season on calm water. It has large crystals and few or no air bubbles, and it can look blue or black when you look down into the water.

White ice (snow ice). White ice forms when snow melts on top of a sheet of ice and refreezes. It is full of air bubbles and smaller crystals. Minnesota DNR says it is only about half as strong as new, clear ice. Double the thickness guidelines on white ice. Michigan DNR describes milky ice from melted and refrozen snow as "often very porous and weak."

Slush. Michigan DNR says to stay off if there is slush on the ice. It says slush ice is only about half as strong as clear ice and shows the ice is no longer freezing from the bottom.

Honeycomb ice. This is mainly a spring-thaw ice. Minnesota DNR calls it one of the most dangerous types of ice. It forms columns, and it "takes little or no effort to shatter it" into pieces. Its rule: "Ice thickness guidelines do not apply to honeycomb ice. If ice is honeycombed, stay off." Michigan DNR says that when ice thaws by day and refreezes at night, the result is weak, honeycombed ice that is unsafe.

Shelf ice. Minnesota DNR says piled, broken chunks may look thick but are very unstable, and air pockets can hide open water.

Minimum thickness for foot travel

Minnesota DNR lists these guidelines for new, clear ice:

• On foot: 4 inches
• Snowmobile or small ATV: 5 to 7 inches
• Side-by-side ATV: 7 to 8 inches
• Small car or SUV: 9 to 10 inches
• Medium SUV or small truck: 11 to 12 inches
• Under 4 inches: stay off

Double these on white ice. Minnesota DNR says the table is for new, clear ice only, based on average equipment weight, and that many other things change ice strength, including air temperature, wind, snow, streams, sun and fish. It does not cover honeycomb ice. The DNR also says it does not measure ice on lakes. Your safety is your responsibility.

When first ice comes

There is no calendar date. It depends on the year's cold. But the order is steady: shallow lakes lock up first and deep lakes take longer. Michigan DNR says deep inland lakes take longer to freeze than shallow lakes. A Minnesota weather story said that in a mild fall, bigger lakes still had "plenty of stored heat to lose" before they would ice over.

Some Minnesota median ice-in dates, from the Minnesota DNR ice-in data (median of dates since 1950):

• Wirth Lake, a small metro lake: November 25.
• Gull Lake, a central Minnesota lake: December 1.
• Lake Minnetonka, a big metro lake: December 8.
• Lake Harriet, a metro lake: December 10.

Half of all years are earlier than the median and half are later. Some lakes ice in weeks off these dates.

Minnesota DNR counts ice-in as when the entire lake is frozen over and the ice cover remains through winter. It also says ice-in dates should not be used to track ice thickness for recreation. Ice-in is a date on a map. It is not a thickness. Local fishing clubs, outfitters and bait shops, Wisconsin DNR says, are the best source for current local ice conditions.

What controls first ice

• Depth and size. Minnesota DNR lists the depth of the water under the ice and the size of the water body as factors in ice strength. Michigan DNR says deep lakes take longer to freeze.
• Snow cover. Snow insulates. Minnesota DNR says it slows freezing and adds weight the ice must carry.
• Currents and springs. Ice over flowing water is often dangerous, especially near streams, bridges and culverts. Wisconsin DNR warns that springs hide under early ice.
• Fish and waterfowl. Minnesota DNR says schools of fish or flocks of waterfowl can adversely affect ice.

How to check ice, step by step

1. Tell someone. Say where you are going and when you expect to return.
2. Go with a partner. Minnesota DNR says it is best to go on the ice only with a buddy.
3. Gear up. Foam life jacket or flotation suit, ice picks, whistle, chisel or drill and tape measure, ice cleats, phone in a waterproof case and rope.
4. Start near shore. Check thickness there first, then stop and check often as you go.
5. Drill and measure. Use a spud bar, auger or drill. Hook the tape on the bottom of the ice. Read the inches.
6. Read the ice. Clear, white, slush or honeycomb? Cracks, dark spots, snow, moving water?
7. Keep measuring. Minnesota DNR says checking as you walk with a chisel is not a substitute for measuring frequently with a tape measure.
8. Turn back if it thins, turns white, or you see slush or open water.

What to carry

Minnesota DNR says a foam life jacket or flotation suit may be the No. 1 item that will keep you alive if you fall through. It says most people who fall through the ice die of drowning, not hypothermia. Ice picks are the second most important item. Your first response to cold water is to gasp and hyperventilate. After you calm your breathing, you have about 10 minutes of meaningful movement to climb out before you lose the feeling and strength to pull yourself out. Also carry a whistle, a chisel or drill, a tape measure, cleats, a phone in a waterproof case and a rope.

If you see someone fall in, stay where you are and do not go to them. Call 911 first. Then throw one end of a rope and have them tie it around themselves.

FAQ

How thick does first ice need to be to walk on?

Minnesota DNR says at least 4 inches of new, clear ice for foot travel. Double that on white ice. Measure it yourself.

What does safe ice look like?

There is no such thing. Clear ice, which can look blue or black, is the strongest. Even so, no ice is ever 100% safe. Check it yourself.

When do lakes lock up in the Upper Midwest?

Shallow lakes tend to freeze first and deep lakes take longer. Minnesota DNR median ice-in dates run from November 25 for Wirth Lake to December 10 for Lake Harriet. Dates vary by year.

Is white ice or slush safe?

No. White ice is about half as strong as clear ice. Michigan DNR says slush is also about half as strong, shows the ice is no longer freezing from the bottom, and to stay off it.

Can I trust a plowed road on early ice?

No. Measure the ice. Minnesota DNR says to stay on plowed ice roads whenever possible and to talk to local experts, but its table still calls for 9 to 10 inches of new, clear ice for a small car or SUV. A plowed road is not a thickness test.