- New clear or black ice is stronger than old ice. A few inches of new ice may be strong enough to support you while a foot or more of old ice may not be.
- Snow on ice will insulate it slowing down the freezing process. The additional weight of the snow can also decrease the weight-bearing capacity of the ice.
- Ice is generally weaker near the shore.
- Ice over moving water can be unsafe especially around inflows and outflows.
- Fluctuations in water level can also weaken ice.
- Ice that begins to thaw is "rotten" and is especially weak in late winter. The ice may be solid on the surface, but may be unsafe due to uneven melting underneath as ice melts or rots from the bottom up.