Lakes U.S. Limestone Trade Down in May Maritime Activity Reports, Inc. June 2, 2026 Source: Lake Carriers' Association Shipments of limestone from U.S. quarries on the Great Lakes decreased 8.1 percent from May of last year to 2.7 million tons. May’s loadings were also below the month’s 5-year average by 5.4 percent. Year-to-date, the Lakes U.S. limestone trade totals 3.9 million tons, a decrease of 14.9 percent compared to 2025 and 15.7 percent below the 5-year average.