When Does Cass Lake Freeze? Ice-In Dates

Short answer: in the Minnesota DNR record, Cass Lake (Beltrami County, near Bemidji) has locked up between November 24 and January 7. The DNR has six entries on file, from 2008 to 2025, and the median is December 4. Four of the six dates fall between December 1 and December 13. That is a thin record, so treat it as a rough window and not a promise.

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

An ice-in date is not a green light. It is the day an observer says the whole lake is frozen and stays that way. It tells you nothing about thickness where you plan to stand.

What the records show

The DNR lists the ice-in records, and each entry names its reporting source (shown in the table below). For Cass Lake (DNR lake ID 04003000, Beltrami County, about 15,958 acres, maximum depth 120 feet) the DNR has:

• 6 entries, from 2008 to 2025.
• Earliest: November 24, 2008.
• Latest: January 7, 2024.
• Median: December 4, as listed by the DNR (since 1950).

The DNR only draws an ice-in map marker for lakes with 20 or more years of record. Cass Lake spans 17 years and has just six dates in them, so it gets no marker and the median rests on very little data.

Cass Lake ice-in dates

The January 7, 2024 entry belongs to the 2023-24 winter. The December 4, 2024 entry belongs to the next one. There are no entries for the other years between 2008 and 2025. We do not know why the January 2024 date is so late, and we will not guess.

Bemidji for comparison

Lake Bemidji is the nearby lake with a long DNR record. The DNR has 80 Bemidji entries from 1958 to 2025, with earliest November 4, 1991, latest December 20, 2001, and a DNR median of November 28. Some years have more than one entry. Recent years:

Bemidji has no 2023 entry. In years both lakes have a date, they land close: 2016 (Dec. 13 and Dec. 9), 2022 (Dec. 1 and Dec. 1), 2025 (Dec. 4 and Dec. 4). That is a small sample. One lake's date is not another's. Check Cass Lake on its own.

What "ice in" means here

The DNR defines ice-in for its citizen observers as the day the entire lake is frozen over and the ice cover remains through winter. The definition can vary from lake to lake. Observers do not report ice thickness.

The DNR says it does not measure ice thickness on Minnesota lakes. It also says the ice-in map is not updated in real time.

So an ice-in date tells you roughly when a lake locked up. It does not tell you what is safe to walk on today.

Ice thickness minimums (Minnesota DNR guideline)

These are the DNR guidelines for new, clear ice only:

• Under 4 inches: stay off.
• 4 inches: ice fishing or other activities on foot.
• 5 to 7 inches: snowmobile or small ATV.
• 7 to 8 inches: side-by-side ATV.
• 9 to 10 inches: small car or SUV.
• 11 to 12 inches: medium SUV or small truck.
• 13 inches: medium truck.
• 16 to 17 inches: heavy-duty truck.
• 20 inches or more: heavy-duty truck with a wheelhouse shelter.

White ice is only about half as strong as new, clear ice. The DNR says to double these numbers on white ice. Ice is seldom the same thickness across a lake. The DNR notes it can be two feet thick in one place and one inch thick a few yards away. Parked loads need thicker ice than moving ones. See the DNR page for those numbers.

How to check current ice

1. Do not rely on a date. Check thickness where you are standing.
2. Drill a hole. Measure clear ice, not slush or white ice.
3. Drill again every few steps. Ice changes fast.
4. Stay off the edges of pressure ridges, cracks, and open water.
5. Wear a flotation device and carry picks and a rope.
6. Tell someone where you are going and when you will be back.

Treat any first ice as unproven until you measure it.

Do not drive onto ice because someone else did. A plowed road is not proof of safe ice. Measure for your own load.

We did not find an official source for a typical start date for the hardwater season or plowed road access on Cass Lake, so we do not give one.

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

What we will update

Iceline will update this guide as new Cass Lake entries are added to the DNR record. Until the record grows, the six dates above are all we have, and most fall between late November and mid December.

FAQ

When does Cass Lake freeze?

In the DNR record it has frozen between November 24 and January 7, with a median of December 4. That is six entries from 2008 to 2025, not a promise for any year.

What is the earliest Cass Lake has frozen?

November 24, 2008. The latest on file is January 7, 2024. The record is short, so an earlier or later date is possible.

How thick should ice be to walk on?

The Minnesota DNR guideline is 4 inches of new, clear ice for ice fishing or other activity on foot. Use 5 to 7 inches for a snowmobile or small ATV. Double the numbers on white ice. Check it yourself.

Does the DNR measure ice thickness on Cass Lake?

No. The DNR says it does not measure ice thickness on Minnesota lakes. Your safety is your responsibility.

Is Bemidji's ice-in date the same as Cass Lake's?

No. Bemidji has a much longer record, with a median of November 28. Use it as a clue only.