When Does Ice Go Out on Lakes? How Ice-Out Happens and How We Forecast It

Short answer: on big northern Minnesota lakes, ice usually goes out in the last week of April or the first week of May. The Minnesota DNR's median ice-out date (since 1950) is April 24 on Mille Lacs, April 27 on Leech, April 30 on Vermilion and May 3 on Lake of the Woods. Farther south it comes sooner. The median on Lake Minnetonka is April 12. Any single year can run weeks early or late.

Ice-out is the day a lake is clear of ice. It is not a fixed rule. The DNR says the meaning varies from lake to lake. For its citizen observers it can mean completely free of ice, or open enough to boat from point A to point B, or about 90 percent free of ice. Observers use the same test every year on their own lake.

Ice-out is the end of hardwater season. The ice gets unsafe weeks before it is gone.

No ice is ever 100% safe. Check it yourself. The Minnesota DNR says it does not measure ice thickness on Minnesota lakes, and that ice-out dates should not be used to track ice thickness for recreation. Iceline's ice-out forecasts are estimates, not a guarantee.

Why ice goes out

Cold builds ice from the top down. Spring takes it apart mostly from the inside and underneath. Here are the pieces.

Sun through the ice. The Minnesota DNR passes along a plain description: in January and February, snow reflects sunlight and insulates the lake. Around March the air warms, the sun gets stronger and the snow melts. Light then gets into the ice. The ice works like greenhouse glass, the water under it warms, and the ice melts from the bottom.

Candling, also called rotten ice. The same DNR page says that when the ice thins to between 4 and 12 inches, it turns into long vertical crystals called candles. They pass light even better, so the ice looks black. Meltwater fills in between the crystals and they start to come apart. A University of Alaska Fairbanks Geophysical Institute article on river breakup explains it the same way: sunlight goes into the ice, the grain boundaries between crystals melt first, and water works down through the cracks to make vertical columns.

Snow cover. Snow on top protects the ice from the sun. Once it melts off, the ice soaks up the sun faster. The Alaska article says ice absorbs solar radiation better than snow does, and wet snow is darker than dry snow, so melting feeds itself.

Wind and open water. The DNR description says the final break is wind. Once the ice is candled and loose, the wind comes up and breaks the surface apart. The candles get blown to one side and pile on shore. The DNR says that can happen in hours. On big lakes like Upper Red, Leech, Lake of the Woods and Mille Lacs, the DNR notes wind and waves already open water and stack up shelf ice during freeze-up and winter, so the wind has a head start in spring.

Inflows and shoreline. The DNR says ice typically melts fastest near shore in spring, because shallow water and plants warm faster there, and rocks, logs and docks soak up heat. It also lists flowing water, streams, culverts and stream inlets as risky spots. The Alaska article adds that meltwater running to the banks speeds up melting along the edge, and shoreline cracks and flooding are often the first sign of breakup. Rivers and creeks coming in bring runoff, and that is why the mouth of a creek goes soft first. (The inflow link is our reading of the DNR and Alaska descriptions, not a measurement.)

What the records say

We read the DNR's ice-out data feed behind its Minnesota Lake Ice Out Dates map (https://www.dnr.state.mn.us/ice_out/index.html). The DNR builds the median from 1950 on. It marks a lake on the map if the record spans 20 or more years. The data comes from citizen observers and agency records, and the DNR says the map is not updated in real time.

The most recent entries in the feed are Mille Lacs April 21, 2026, Leech April 26, 2026, Vermilion April 28, 2026, Lake of the Woods May 15, 2026 and Minnetonka April 3, 2026. The "earliest" and "latest" columns cover each lake's whole record, which starts at different years. Compare them to the median, not to each other.

The spread is the point. On Mille Lacs, earliest and latest are about two months apart. That is why a median is a place to start, not a plan.

Lakes outside Minnesota. The National Snow and Ice Data Center (NSIDC) holds the Global Lake and River Ice Phenology Database. NSIDC says it covers 865 lakes and rivers in the Northern Hemisphere, with freeze and breakup dates. We read its freeze/thaw table and pulled the breakup dates for four lakes:

Those are extremes from long records, not what to expect this year.

Why late-season ice is unsafe even when thick

Thickness numbers are for new, clear ice. Rotten ice does not follow them. The Minnesota DNR says honeycomb ice is one of the most dangerous types and is tied to many fall-throughs late in the ice season. It forms when thaw water seeps into cracks and the ice breaks into columns that can shatter with little or no effort. The DNR says thickness guidelines do not apply to honeycomb ice, and to stay off it.

Spring ice also fools you:

• It can be a foot thick and still be candled.
• It melts first near shore, so the walk back to the landing is often the worst part.
• Inlets, creek mouths and current spots go soft first.
• Wind can move a loose sheet or open a lead fast.

When the landing gets sloppy, the season is over. See our ice thickness chart and pressure ridges, cracks and slush guides.

How Iceline forecasts, in plain words

Iceline's forecasts are estimates. Here is the outline of the method family they come from. The ice-growth side is standard, sourced science.

1. Count the cold. A freezing degree day is 32 minus the day's average air temperature in degrees F (NOAA's Alaska-Pacific River Forecast Center uses FDD = 32 minus Ta). Add the days up through the winter.
2. Turn cold into inches. The Army's Cold Regions Research and Engineering Laboratory (CRREL) gives the modified Stefan equation as thickness in inches = C x (accumulated freezing degree days) to the 0.5 power. CRREL says C usually falls between 0.3 and 0.6 and lists 0.8 for a windy lake with no snow and 0.5 to 0.7 for an average lake with snow. At C = 0.6, 300 freezing degree days gives about 10 inches.
3. Account for snow. CRREL says snow insulates the ice and lowers the effective coefficient. Snow-covered ice grows slower than bare ice.
4. Spring side. In spring the question flips from growth to decay. Warm days, sun and snow-free ice speed up rot, as described above. Treat any ice-out date as a window, not a single day.

We have a separate guide on the coefficients, how fast ice grows.

What a forecast cannot do. It does not know about the spring under your hole, the creek mouth, the drift or the pressure ridge. It does not replace a drill, a spud and your own eyes. A forecast tells you when to start looking. The ice tells you where to stand. Iceline forecasts are estimates, not a guarantee.

FAQ

When does ice go out on Minnesota lakes?

The DNR's median dates since 1950 run from mid-April on southern lakes (Minnetonka April 12) to early May on the far north (Lake of the Woods May 3). Individual years vary by weeks.

What is ice-out?

The day a lake is clear of ice. The DNR says the exact meaning differs by lake: fully free of ice, boat-navigable, or about 90 percent free.

What is candled ice?

Rotten ice where the sheet has broken into long vertical crystals. It can be thick and still hold nothing. Stay off.

Is thick ice safe in April?

Not by thickness alone. Thickness guidelines do not apply to honeycomb ice. No ice is ever 100% safe. Check it yourself, and in late season, stay off.

Can Iceline tell me the exact ice-out day?

No. Iceline forecasts are estimates, not a guarantee. Dates move with weather.