Guide

Go seeLandscape

Border ice along the edges of a stream

January to February

After a spell of cold days and nights, a stream can freeze along its banks and in slow water while the faster middle can stay open. This rim of ice is called border ice or shore ice, and you can look at it from dry ground.

Why this time of year

Border ice starts in the shallow, slower water at the sides of a river or stream once the weather has stayed cold, so a run of freezing days is when a stream gets a rim of ice.

How to notice it

  1. From dry ground well back from the bank, find a stream and look at which parts are frozen. Compare the slow, shallow edges with the fast middle.
  2. Look at where the ice stops. Notice whether the open water is where the stream moves fastest.
  3. On a later visit, check whether the water has dropped. A sheet of ice can stay put with a gap of air under it where the water used to be.

Try this with kids: Which part of the stream froze first, the edges or the middle? Why do you think the fast part stayed open?

Phrase to know: “Border ice” is ice that forms along and is attached to the shore, without reaching all the way across the water.

Safety

  • Look from dry ground only. Never walk or stand on stream or river ice: ice over moving water is generally weaker than ice over still water.
  • Keep children close and dogs on a leash near the water.

Sources

  • weather.govNWS slide deck: border ice is ice formed along and fastened to the shore that does not extend across the entire river (AKA shore ice); forms in shallower, slower-moving water on the river sides, usually when daily average temp is below 20F; expands from both sides as cold continues.
  • dee.nebraska.govUS Army CRREL Ice Engineering bulletin 15 (1997) glossary: border ice formed along and fastened to the shore, does not extend across the river, also called shore ice.
  • usgs.govUSGS photo caption, Libby Brook, Maine (2005): a gap between the water level and a layer of ice above.
  • hcam.tvReprint of 2018 Massachusetts DCR / State Police / MEMA / Fire Services release: ice formed over flowing water is generally weaker than ice over still water.

Checked against these sources on October 9, 2026.

In the guide for January, February

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