The U.S. Coast Guard says warming temperatures this weekend could pose safety issues on Lake Michigan and frozen inland rivers, streams and ponds. The Coast Guard is urging people to use extreme caution on the water and melting ice. Ice thickness can vary, even in small areas. Water currents around narrow spots, bridges, inlets and outlets can cause thinner ice. The Coast Guard says stay away from cracks, seams, pressure ridges, slushy areas and darker areas. Ice near the shore of a frozen lake may be unsafe and weaker because of shifting, expansion and sunlight reflecting off the bottom. A majority of Coast Guard units around Lake Michigan have winterized their rescue boats. That means the Coast Guard has a reduced ability to respond to anyone in distress on the water.