Lakeland is a city in Polk County, Florida, United States, located just outside of Tampa. According to the 2013 U.S. Census Bureau estimate, the city had a population of 100,710. Lakeland is a principal city of the Lakeland-Winter Haven Metropolitan Statistical Area (coterminous with Polk County), which had an estimated population of 623,009 in July 2013 based on data from the University of Florida Bureau of Economic and Business Research. It is twinned with Richmond Hill, Ontario, Canada; Imabari, Ehime, Japan; Balti, Moldova; Portmore, Jamaica; and Chongming County, Shanghai, China as part of the Sister Cities program. The dominant feature in Lakeland is the city's many lakes. Thirty-eight lakes are named, with a number of other bodies of water unnamed, mostly phosphate mine pits that eventually filled with water. The largest of these is Lake Parker, which is 2,550 acres (10.3 km2) in size. Much of the culture of Lakeland revolves around its many lakes, and many people use the lakes as reference points in much the same way that people in other towns use streets as reference points, such as "I live near Lake Beulah." In addition to Lake Parker, some of the more prominent lakes in the Lakeland area are Lake Hollingsworth, Lake Morton, Lake Mirror, and Lake Gibson. Swans are one of the most visible features on the lakes of Lakeland. They have a long history, the first swans appearing around 1923. By 1954, the swans were gone, eradicated by alligators and pets. A Lakeland resident who mourned the passing of the swans wrote to Queen Elizabeth. The royal family allowed the capture of two of the royal swans, and the swans now on the lakes of Lakeland are the descendants of the royal swans sent by the queen. In July 2006, Scott Lake, one of the city's lakes, was almost totally drained by a cluster of sinkholes. The lake later partially refilled.