Water levels on U.S. Midwest rivers were rising after recent warm temperatures and weekend rains mixed with snow hit the upper Midwest but no navigational problems were expected, river officials said. "We're experiencing a bubble effect with a rise and fall of water -- which will continue over the next couple of days," said Lt. Chris O'Neil, spokesman for the U.S. Coast Guard in St. Louis. Water levels on the upper-Mississippi River near St. Louis were more than three times levels reached a week ago but were expected to drop gradually by Wednesday, said Charles Camillo, U.S. Army Corps of Engineers spokesman at St. Louis. "Water was forecast to reach 20.5 feet on Monday, then drop to 19.3 feet on Tuesday and 17.1 on Wednesday at the St. Louis gauge," Camillo said.