New ice is usually stronger than old ice. As ice ages, the bond between the crystals decays, making it weaker, even if melting has not occurred.
Ice formed over flowing water (rivers or lakes containing a large number of springs) is generally 15% weaker.
Never go onto the ice alone. A friend may be able to rescue you or go for help if you fall through the ice.
Always keep your pets on a leash. If a pet falls through the ice do not attempt to rescue your pet, call 9-1-1 or go for help.
Read the complete MEMA memo on ice safety!