Water Levels Decline NPR's David Welna reports from Chicago that water levels in the Great Lakes have dropped by more than a foot and a half during the last year. Experts say it's not unusual for Great Lakes water levels to rise and fall, as part of natural cycles. The most immediate effect of receding water levels is on navigation. Cargo ships have lowered the amount of tonnage that they haul. Recreational boaters are more likely to hit sandbars.