Ice Hazards and Features

Ice hazards come in many forms and many of them are more common at different parts of the season.  Some users are impacted by specific features more than others.  The following are lists of things to consider in different circumstances. 

New Ice:

Ice Fever is tends to be strongest with new, smooth black ice.  It is also the most common time to fall through.  Some common hazards include: 


Mid Season-thick cold ice (6" and up)

Big Ice

  • Leeds
  • Jumbled ice, Ice sharks and other forms of disrupted ice. See Glossary
  • Pressure ridges of all types
  • Random thin spots associated with disrupted ice and folded ridges.
  • Risk of large sections of an ice sheet blowing into open water, sometimes in supprisingly little wind.
  • Sieches and underwater currents may be a factor on some lakes.  
  • Risk of large scale, rapid break up of moderately thin ice on big water
  • Polynays (big open areas)
  • For more see the Big Ice and New Big Ice pages
  • If you get wet or hurt several miles from shore, getting off can take a while. 

 Early Season Thaws

  • Thin ice thaws and weakens more quickly than thick ice
  • Gas holes deroof and can become holes up to several feet in diameter
  • Seeded ice has small crystals (one inch or less) and it weakens especially quickly in sunny thaws. 
  • Drain holes
  • Melted out ridges
  • Drift holes (form near thicker drifts)
  • Reef holes
  • Shell ice
  • Puddle Holes
  • Wind holes
  • Leads, finger rafting and other big ice situations
  • Re-opening of ice covered areas and holes.

Thick Ice Thaws

Snow Covered Ice

  • Snow is a good insulator so even a small amount significantly slows the growth of the underlying ice or allows currents to erode the ice faster than it thickens.
  • Submergence of ice by the weight of a snow cover over the ice often results in a thick slush layer under snow.  This makes travel messy and difficult 
  • Slush holes:  slush over open water.  These are usually not common but can be treacherous.
  • You can't see most of the things that would serve as warning signs on snow free ice.
  • Gas hole roofs are likely to melt with an insulating blanket of snow. 
  • Some snow drifts may be snow caps on gas holes.  These somtimes look a little more granular than nearby drifts.
  • Blowing snow fills open water at pressure ridges.  This can make them look more solid than they are, especially in the first few days when the slush has not frozen yet.

End of season

  • The temptations of nice weather and one more day on the ice.
  • Late season new black ice can weaken very quickly in the strong spring sun.
  • Spring tectonic cracks
  • Porous ice-when the puddles disappear
  • Thaw progression
  • Thinning and melting along the shore
  • Weakened and broken ice at vehicle access points
  • Rising lake levels move the shoreline away from the ice sheet.
  • More gas holes
  • Weed holes (see glossary)
  • Big ice: leads, detached plates, etc.
  • Thin ice along the shoreline, rising water levels,
  • Large grain vs small grain ice
  • Overnight temperatures frequently makes the ice appear to be good in the morning.   This lures people onto the ice one last time.  A few hours later it can be so weak it will not hold up a person on foot, let alone a vehicle. This is more likely with small grain ice (S2).

Ice over flowing water:

  • River and stream ice is complicated  with currents, variable water depth and water temperature.  This can result in highly variable ice thickness.
  • Even at  low flow rates, impoundments tend to have thin areas in places where you would not expect them if there was no flow.  This is particularly true early and late in the season.
  • Snow cover on river ice makes problems harder to find and insulates the ice from cooling by cold  weather and enhances under-ice erosion. 
  • Passages between large bodies of water are typically thinner and melt away more quickly than water with no flow.  This is especially pronounced if one of the water bodies does not have an ice cover.  
  • Stream/river inlets  and outlets are common sources of problems.  The ice thickness near them can be highly variable depending on the particular circumstances at the time. 
  • Deltas may have under-ice erosion from the shallow water and/or the temperature of the incoming stream.   Gas holes are very common in the underwater parts of deltas, often in areas that are not the current outlet for the river/stream.
  • Bubblers and dock protection systems often skin over at night or over a few days when they are turned off to save electricity.  Approach docks and moored boats accordingly.

Shallow Ponds:

  • Shallow ponds tend to melt faster from the bottom than ice over deeper water
  • They often melt completely well before ice over deeper water.
  • They are generally not a good choice for late season ice activities.


  • Swamps are often riddled with thin ice when the ice on a lake adjoining the swamp is fine.
  • Swamps are often deeper in places than you might expect
  • The ice within 50 or so feet of the edge of a swamp is more likely to have thin ice, especially early in the season.

 Salt Ice:

  • We defer to the Swedes and sailors on Long Island and on the Jersey Shore as they have a great deal of experience skating and sailing on salt ice.   
  • In general salt ice is weaker,  thaws at lower temperatures and is harder to read than lake ice.
  •  And  there are tides, swells and shipping traffic.